按字符串属性值排序对象数组
I have an array of JavaScript objects:
var objs = [
{ first_nom: 'Lazslo', last_nom: 'Jamf' },
{ first_nom: 'Pig', last_nom: 'Bodine' },
{ first_nom: 'Pirate', last_nom: 'Prentice' }
];
How can I sort them by the value of last_nom in JavaScript?
I know about sort(a,b), but that only seems to work on strings and numbers. Do I need to add a toString() method to my objects?
转载于:https://stackoverflow.com/questions/1129216/sort-array-of-objects-by-string-property-value
It's easy enough to write your own comparison function:
function compare(a,b) {
if (a.last_nom < b.last_nom)
return -1;
if (a.last_nom > b.last_nom)
return 1;
return 0;
}
objs.sort(compare);
Or inline (c/o Marco Demaio):
objs.sort((a,b) => (a.last_nom > b.last_nom) ? 1 : ((b.last_nom > a.last_nom) ? -1 : 0));
If you have duplicate last names you might sort those by first name-
obj.sort(function(a,b){
if(a.last_nom< b.last_nom) return -1;
if(a.last_nom >b.last_nom) return 1;
if(a.first_nom< b.first_nom) return -1;
if(a.first_nom >b.first_nom) return 1;
return 0;
});
Instead of using a custom comparison function, you could also create an object type with custom toString() method (which is invoked by the default comparison function):
function Person(firstName, lastName) {
this.firtName = firstName;
this.lastName = lastName;
}
Person.prototype.toString = function() {
return this.lastName + ', ' + this.firstName;
}
var persons = [ new Person('Lazslo', 'Jamf'), ...]
persons.sort();
You can also create a dynamic sort function that sorts objects by their value that you pass:
function dynamicSort(property) {
var sortOrder = 1;
if(property[0] === "-") {
sortOrder = -1;
property = property.substr(1);
}
return function (a,b) {
var result = (a[property] < b[property]) ? -1 : (a[property] > b[property]) ? 1 : 0;
return result * sortOrder;
}
}
So you can have an array of objects like this:
var People = [
{Name: "Name", Surname: "Surname"},
{Name:"AAA", Surname:"ZZZ"},
{Name: "Name", Surname: "AAA"}
];
...and it will work when you do:
People.sort(dynamicSort("Name"));
People.sort(dynamicSort("Surname"));
People.sort(dynamicSort("-Surname"));
Actually this already answers the question. Below part is written because many people contacted me, complaining that it doesn't work with multiple parameters.
Multiple Parameters
You can use the function below to generate sort functions with multiple sort parameters.
function dynamicSortMultiple() {
/*
* save the arguments object as it will be overwritten
* note that arguments object is an array-like object
* consisting of the names of the properties to sort by
*/
var props = arguments;
return function (obj1, obj2) {
var i = 0, result = 0, numberOfProperties = props.length;
/* try getting a different result from 0 (equal)
* as long as we have extra properties to compare
*/
while(result === 0 && i < numberOfProperties) {
result = dynamicSort(props[i])(obj1, obj2);
i++;
}
return result;
}
}
Which would enable you to do something like this:
People.sort(dynamicSortMultiple("Name", "-Surname"));
Adding It To The Prototype
(Implementation which is just below is inspired from Mike R's answer)
I wouldn't recommend changing a native object prototype but just to give an example so you can implement it on your own objects (For the environments that support it, you can also use Object.defineProperty as shown in the next section, which at least doesn't have the negative side-effect of being enumerable, as described at the last part)
Prototype implementation would be something like the following (Here's a working example):
//Don't just copy-paste this code. You will break the "for-in" loops
!function() {
function _dynamicSortMultiple(attr) {
/* dynamicSortMultiple function body comes here */
}
function _dynamicSort(property) {
/* dynamicSort function body comes here */
}
Array.prototype.sortBy = function() {
return this.sort(_dynamicSortMultiple.apply(null, arguments));
}
}();
The "OK" Way Of Adding It To The Prototype
If you're targeting IE v9.0 and up then, as I previously mentioned, use Object.defineProperty like this (working example):
//Won't work below IE9, but totally safe otherwise
!function() {
function _dynamicSortMultiple(attr) {
/* dynamicSortMultiple function body comes here */
}
function _dynamicSort(property) {
/* dynamicSort function body comes here */
}
Object.defineProperty(Array.prototype, "sortBy", {
enumerable: false,
writable: true,
value: function() {
return this.sort(_dynamicSortMultiple.apply(null, arguments));
}
});
}();
This can be an acceptable compromise until the bind operator arrives.
All those prototype fun enables this:
People.sortBy("Name", "-Surname");
You Should Read This
If you use the direct prototype access method (Object.defineProperty is fine) and other code does not check hasOwnProperty, kittens die! Ok, to be honest, no harm comes to any kitten really but probably things will break and every other developer in your team will hate you:
See that last "SortBy"? Yeah. Not cool. Use Object.defineProperty where you can, and leave the Array.prototype alone otherwise.
use underscore, its small and awesome...
sortBy_.sortBy(list, iterator, [context]) Returns a sorted copy of list, ranked in ascending order by the results of running each value through iterator. Iterator may also be the string name of the property to sort by (eg. length).
var objs = [
{ first_nom: 'Lazslo',last_nom: 'Jamf' },
{ first_nom: 'Pig', last_nom: 'Bodine' },
{ first_nom: 'Pirate', last_nom: 'Prentice' }
];
var sortedObjs = _.sortBy( objs, 'first_nom' );
Simple and quick solution to this problem using prototype inheritance:
Array.prototype.sortBy = function(p) {
return this.slice(0).sort(function(a,b) {
return (a[p] > b[p]) ? 1 : (a[p] < b[p]) ? -1 : 0;
});
}
Example / Usage
objs = [{age:44,name:'vinay'},{age:24,name:'deepak'},{age:74,name:'suresh'}];
objs.sortBy('age');
// Returns
// [{"age":24,"name":"deepak"},{"age":44,"name":"vinay"},{"age":74,"name":"suresh"}]
objs.sortBy('name');
// Returns
// [{"age":24,"name":"deepak"},{"age":74,"name":"suresh"},{"age":44,"name":"vinay"}]
Update: No longer modifies original array.
additional desc params for Ege Özcan code
function dynamicSort(property, desc) {
if (desc) {
return function (a, b) {
return (a[property] > b[property]) ? -1 : (a[property] < b[property]) ? 1 : 0;
}
}
return function (a, b) {
return (a[property] < b[property]) ? -1 : (a[property] > b[property]) ? 1 : 0;
}
}
Combining Ege's dynamic solution with Vinay's idea, you get a nice robust solution:
Array.prototype.sortBy = function() {
function _sortByAttr(attr) {
var sortOrder = 1;
if (attr[0] == "-") {
sortOrder = -1;
attr = attr.substr(1);
}
return function(a, b) {
var result = (a[attr] < b[attr]) ? -1 : (a[attr] > b[attr]) ? 1 : 0;
return result * sortOrder;
}
}
function _getSortFunc() {
if (arguments.length == 0) {
throw "Zero length arguments not allowed for Array.sortBy()";
}
var args = arguments;
return function(a, b) {
for (var result = 0, i = 0; result == 0 && i < args.length; i++) {
result = _sortByAttr(args[i])(a, b);
}
return result;
}
}
return this.sort(_getSortFunc.apply(null, arguments));
}
Usage:
// Utility for printing objects
Array.prototype.print = function(title) {
console.log("************************************************************************");
console.log("**** "+title);
console.log("************************************************************************");
for (var i = 0; i < this.length; i++) {
console.log("Name: "+this[i].FirstName, this[i].LastName, "Age: "+this[i].Age);
}
}
// Setup sample data
var arrObj = [
{FirstName: "Zach", LastName: "Emergency", Age: 35},
{FirstName: "Nancy", LastName: "Nurse", Age: 27},
{FirstName: "Ethel", LastName: "Emergency", Age: 42},
{FirstName: "Nina", LastName: "Nurse", Age: 48},
{FirstName: "Anthony", LastName: "Emergency", Age: 44},
{FirstName: "Nina", LastName: "Nurse", Age: 32},
{FirstName: "Ed", LastName: "Emergency", Age: 28},
{FirstName: "Peter", LastName: "Physician", Age: 58},
{FirstName: "Al", LastName: "Emergency", Age: 51},
{FirstName: "Ruth", LastName: "Registration", Age: 62},
{FirstName: "Ed", LastName: "Emergency", Age: 38},
{FirstName: "Tammy", LastName: "Triage", Age: 29},
{FirstName: "Alan", LastName: "Emergency", Age: 60},
{FirstName: "Nina", LastName: "Nurse", Age: 54}
];
//Unit Tests
arrObj.sortBy("LastName").print("LastName Ascending");
arrObj.sortBy("-LastName").print("LastName Descending");
arrObj.sortBy("LastName", "FirstName", "-Age").print("LastName Ascending, FirstName Ascending, Age Descending");
arrObj.sortBy("-FirstName", "Age").print("FirstName Descending, Age Ascending");
arrObj.sortBy("-Age").print("Age Descending");
You may need to convert them to the lower case in order to prevent from confusion.
objs.sort(function (a,b) {
var nameA=a.last_nom.toLowerCase(), nameB=b.last_nom.toLowerCase()
if (nameA < nameB)
return -1;
if (nameA > nameB)
return 1;
return 0; //no sorting
})
Don't get why people make it so complicated:
objs.sort(function(a, b){
return a.last_nom > b.last_nom;
});
For stricter engines:
objs.sort(function(a, b){
return a.last_nom == b.last_nom ? 0 : +(a.last_nom > b.last_nom) || -1;
});
Swap the operator to have it sorted by reverse alphabetical order.
Example Usage:
objs.sort(sortBy('last_nom'));
Script:
/**
* @description
* Returns a function which will sort an
* array of objects by the given key.
*
* @param {String} key
* @param {Boolean} reverse
* @return {Function}
*/
function sortBy(key, reverse) {
// Move smaller items towards the front
// or back of the array depending on if
// we want to sort the array in reverse
// order or not.
var moveSmaller = reverse ? 1 : -1;
// Move larger items towards the front
// or back of the array depending on if
// we want to sort the array in reverse
// order or not.
var moveLarger = reverse ? -1 : 1;
/**
* @param {*} a
* @param {*} b
* @return {Number}
*/
return function(a, b) {
if (a[key] < b[key]) {
return moveSmaller;
}
if (a[key] > b[key]) {
return moveLarger;
}
return 0;
};
}
Acording your example, you need to sort by two fields (last name, first name), rather then one. You can use Alasql library to make this sort in one line:
var res = alasql('SELECT * FROM ? ORDER BY last_nom, first_nom',[objs]);
Try this example at jsFiddle.
I Just enhanced Ege Özcan's dynamic sort to dive deep inside objects. If Data looks like this:
obj = [
{
a: { a: 1, b: 2, c: 3 },
b: { a: 4, b: 5, c: 6 }
},
{
a: { a: 3, b: 2, c: 1 },
b: { a: 6, b: 5, c: 4 }
}];
and if you want to sort it over a.a property I think my enhancement helps very well. I add new functionality to objects like this:
Object.defineProperty(Object.prototype, 'deepVal', {
enumerable: false,
writable: true,
value: function (propertyChain) {
var levels = propertyChain.split('.');
parent = this;
for (var i = 0; i < levels.length; i++) {
if (!parent[levels[i]])
return undefined;
parent = parent[levels[i]];
}
return parent;
}
});
and changed _dynamicSort's return function:
return function (a,b) {
var result = ((a.deepVal(property) > b.deepVal(property)) - (a.deepVal(property) < b.deepVal(property)));
return result * sortOrder;
}
And now you can sort by a.a. this way:
obj.sortBy('a.a');
See Commplete script in JSFiddle
Sorting (more) Complex Arrays of Objects
Since you probably encounter more complex data structures like this array, I would expand the solution.
TL;DR
Are more pluggable version based on @ege-Özcan's very lovely answer.
Problem
I encountered the below and couldn't change it. I also did not want to flatten the object temporarily. Nor did I want to use underscore / lodash, mainly for performance reasons and the fun to implement it myself.
var People = [
{Name: {name: "Name", surname: "Surname"}, Middlename: "JJ"},
{Name: {name: "AAA", surname: "ZZZ"}, Middlename:"Abrams"},
{Name: {name: "Name", surname: "AAA"}, Middlename: "Wars"}
];
Goal
The goal is to sort it primarily by People.Name.name and secondarily by People.Name.surname
Obstacles
Now, in the base solution uses bracket notation to compute the properties to sort for dynamically. Here, though, we would have to construct the bracket notation dynamically also, since you would expect some like People['Name.name'] would work - which doesn't.
Simply doing People['Name']['name'], on the other hand, is static and only allows you to go down the n-th level.
Solution
The main addition here will be to walk down the object tree and determine the value of the last leaf, you have to specify, as well as any intermediary leaf.
var People = [
{Name: {name: "Name", surname: "Surname"}, Middlename: "JJ"},
{Name: {name: "AAA", surname: "ZZZ"}, Middlename:"Abrams"},
{Name: {name: "Name", surname: "AAA"}, Middlename: "Wars"}
];
People.sort(dynamicMultiSort(['Name','name'], ['Name', '-surname']));
// Results in...
// [ { Name: { name: 'AAA', surname: 'ZZZ' }, Middlename: 'Abrams' },
// { Name: { name: 'Name', surname: 'Surname' }, Middlename: 'JJ' },
// { Name: { name: 'Name', surname: 'AAA' }, Middlename: 'Wars' } ]
// same logic as above, but strong deviation for dynamic properties
function dynamicSort(properties) {
var sortOrder = 1;
// determine sort order by checking sign of last element of array
if(properties[properties.length - 1][0] === "-") {
sortOrder = -1;
// Chop off sign
properties[properties.length - 1] = properties[properties.length - 1].substr(1);
}
return function (a,b) {
propertyOfA = recurseObjProp(a, properties)
propertyOfB = recurseObjProp(b, properties)
var result = (propertyOfA < propertyOfB) ? -1 : (propertyOfA > propertyOfB) ? 1 : 0;
return result * sortOrder;
};
}
/**
* Takes an object and recurses down the tree to a target leaf and returns it value
* @param {Object} root - Object to be traversed.
* @param {Array} leafs - Array of downwards traversal. To access the value: {parent:{ child: 'value'}} -> ['parent','child']
* @param {Number} index - Must not be set, since it is implicit.
* @return {String|Number} The property, which is to be compared by sort.
*/
function recurseObjProp(root, leafs, index) {
index ? index : index = 0
var upper = root
// walk down one level
lower = upper[leafs[index]]
// Check if last leaf has been hit by having gone one step too far.
// If so, return result from last step.
if (!lower) {
return upper
}
// Else: recurse!
index++
// HINT: Bug was here, for not explicitly returning function
// https://stackoverflow.com/a/17528613/3580261
return recurseObjProp(lower, leafs, index)
}
/**
* Multi-sort your array by a set of properties
* @param {...Array} Arrays to access values in the form of: {parent:{ child: 'value'}} -> ['parent','child']
* @return {Number} Number - number for sort algorithm
*/
function dynamicMultiSort() {
var args = Array.prototype.slice.call(arguments); // slight deviation to base
return function (a, b) {
var i = 0, result = 0, numberOfProperties = args.length;
// REVIEW: slightly verbose; maybe no way around because of `.sort`-'s nature
// Consider: `.forEach()`
while(result === 0 && i < numberOfProperties) {
result = dynamicSort(args[i])(a, b);
i++;
}
return result;
}
}
Example
Working example on JSBin
function compare(propName) {
return function(a,b) {
if (a[propName] < b[propName])
return -1;
if (a[propName] > b[propName])
return 1;
return 0;
};
}
objs.sort(compare("last_nom"));
This is a simple problem, don't know why people have such complex solution.
A simple sort function (based on quick-sort algorithm):
function sortObjectsArray(objectsArray, sortKey)
{
// Quick Sort:
var retVal;
if (1 < objectsArray.length)
{
var pivotIndex = Math.floor((objectsArray.length - 1) / 2); // middle index
var pivotItem = objectsArray[pivotIndex]; // value in the middle index
var less = [], more = [];
objectsArray.splice(pivotIndex, 1); // remove the item in the pivot position
objectsArray.forEach(function(value, index, array)
{
value[sortKey] <= pivotItem[sortKey] ? // compare the 'sortKey' proiperty
less.push(value) :
more.push(value) ;
});
retVal = sortObjectsArray(less, sortKey).concat([pivotItem], sortObjectsArray(more, sortKey));
}
else
{
retVal = objectsArray;
}
return retVal;
}
Use example:
var myArr =
[
{ val: 'x', idx: 3 },
{ val: 'y', idx: 2 },
{ val: 'z', idx: 5 },
];
myArr = sortObjectsArray(myArr, 'idx');
A simple way:
objs.sort(function(a,b) {
return b.last_nom.toLowerCase() < a.last_nom.toLowerCase();
});
See that '.toLowerCase()' is necessary to prevent erros in comparing strings.
In ES6/ES2015 or later you can do this way:
objs.sort((a, b) => a.last_nom.localeCompare(b.last_nom));
objs.sort(function(a,b){return b.last_nom>a.last_nom})
There are many good answers here, but I would like to point out that they can be extended very simply to achieve a lot more complex sorting. The only thing you have to do is to use the OR operator to chain comparision functions like this:
objs.sort((a,b)=> fn1(a,b) || fn2(a,b) || fn3(a,b) )
Where fn1, fn2, ... are the sort functions which return [-1,0,1]. This results in "sorting by fn1", "sorting by fn2" which is pretty much equal to ORDER BY in SQL.
This solution is based on the behaviour of || operator which evaluates to the first evaluated expression which can be converted to true.
The simplest form has only one inlined function like this:
// ORDER BY last_nom
objs.sort((a,b)=> a.last_nom.localeCompare(b.last_nom) )
Having two steps with last_nom,first_nom sort order would look like this:
// ORDER_BY last_nom, first_nom
objs.sort((a,b)=> a.last_nom.localeCompare(b.last_nom) ||
a.first_nom.localeCompare(b.first_nom) )
A generic comparision function could be something like this:
// ORDER BY <n>
let cmp = (a,b,n)=>a[n].localeCompare(b[n])
This function could be extended to support numeric fields, case sensitity, arbitary datatypes etc.
You can them use it with chaining them by sort priority:
// ORDER_BY last_nom, first_nom
objs.sort((a,b)=> cmp(a,b, "last_nom") || cmp(a,b, "first_nom") )
// ORDER_BY last_nom, first_nom DESC
objs.sort((a,b)=> cmp(a,b, "last_nom") || -cmp(a,b, "first_nom") )
// ORDER_BY last_nom DESC, first_nom DESC
objs.sort((a,b)=> -cmp(a,b, "last_nom") || -cmp(a,b, "first_nom") )
The point here is that pure JavaScript with functional approach can take you a long way without external libraries or complex code. It is also very effective, since no string parsing have to be done
One more option:
var someArray = [...];
function generateSortFn(prop, reverse) {
return function (a, b) {
if (a[prop] < b[prop]) return reverse ? 1 : -1;
if (a[prop] > b[prop]) return reverse ? -1 : 1;
return 0;
};
}
someArray.sort(generateSortFn('name', true));
sorts ascending by default.
I know this question is too old, but I didn't see any implementation similar to mine.
This version is based on the Schwartzian transform idiom.
function sortByAttribute(array, ...attrs) {
// generate an array of predicate-objects contains
// property getter, and descending indicator
let predicates = attrs.map(pred => {
let descending = pred.charAt(0) === '-' ? -1 : 1;
pred = pred.replace(/^-/, '');
return {
getter: o => o[pred],
descend: descending
};
});
// schwartzian transform idiom implementation. aka: "decorate-sort-undecorate"
return array.map(item => {
return {
src: item,
compareValues: predicates.map(predicate => predicate.getter(item))
};
})
.sort((o1, o2) => {
let i = -1, result = 0;
while (++i < predicates.length) {
if (o1.compareValues[i] < o2.compareValues[i]) result = -1;
if (o1.compareValues[i] > o2.compareValues[i]) result = 1;
if (result *= predicates[i].descend) break;
}
return result;
})
.map(item => item.src);
}
Here's an example how to use it:
let games = [
{ name: 'Pako', rating: 4.21 },
{ name: 'Hill Climb Racing', rating: 3.88 },
{ name: 'Angry Birds Space', rating: 3.88 },
{ name: 'Badland', rating: 4.33 }
];
// sort by one attribute
console.log(sortByAttribute(games, 'name'));
// sort by mupltiple attributes
console.log(sortByAttribute(games, '-rating', 'name'));
Using Ramda,
npm install ramda
import R from 'ramda'
var objs = [
{ first_nom: 'Lazslo', last_nom: 'Jamf' },
{ first_nom: 'Pig', last_nom: 'Bodine' },
{ first_nom: 'Pirate', last_nom: 'Prentice' }
];
var ascendingSortedObjs = R.sortBy(R.prop('last_nom'), objs)
var descendingSortedObjs = R.reverse(ascendingSortedObjs)
Lodash.js (superset of Underscore.js)
It's good not to add a framework for every simple piece of logic, but relying on a well tested utility frameworks, speed up development and reduce the amount of bugs written is no shame.
Lodash produces very clean code and promotes a more functional programming style, which results in less bugs. In one glimpse it becomes clear what the intent if the code is.
OP's issue can simply be solved as:
const sortedObjs = _.sortBy(objs, 'last_nom');
More info? E.g. we have following nested object:
const users = [
{ 'user': {'name':'fred', 'age': 48}},
{ 'user': {'name':'barney', 'age': 36 }},
{ 'user': {'name':'wilma'}},
{ 'user': {'name':'betty', 'age': 32}}
];
We now can use the _.property shorthand user.age to specify the path to the property that should be matched. We will sort the user objects by the nested age property. Yes, it allows for nested property matching!
const sortedObjs = _.sortBy(users, ['user.age']);
Want it reversed? No problem. Use _.reverse.
const sortedObjs = _.reverse(_.sortBy(users, ['user.age']));
Want to combine both using Chaining instead?
const sortedObjs = _.chain(users).sortBy('user.age').reverse().value();
I have a piece of code that works for me:
arr.sort((a, b) => a.name > b.name)
UPDATE: Not working always, so it is not correct :(
Given the original example:
var objs = [
{ first_nom: 'Lazslo', last_nom: 'Jamf' },
{ first_nom: 'Pig', last_nom: 'Bodine' },
{ first_nom: 'Pirate', last_nom: 'Prentice' }
];
Sort by multiple fields:
objs.sort(function(left, right) {
var last_nom_order = left.last_nom.localeCompare(right.last_nom);
var first_nom_order = left.first_nom.localeCompare(right.first_nom);
return last_nom_order || first_nom_order;
});
Notes
a.localeCompare(b)is universally supported and returns -1,0,1 ifa<b,a==b,a>brespectively.||in the last line giveslast_nompriority overfirst_nom.- Subtraction works on numeric fields:
var age_order = left.age - right.age; - Negate to reverse order,
return -last_nom_order || -first_nom_order || -age_order;
Using lodash or Underscore, its a piece of cake
> const sortedList = _.orderBy(objs, [last_nom], [asc]); // asc or desc
Way 1 :
You can use Underscore.js. Import underscore first.
import * as _ from 'underscore';
let SortedObjs = _.sortBy(objs, 'last_nom');
Way 2 : Use compare function.
function compare(first, second) {
if (first.last_nom < second.last_nom)
return -1;
if (first.last_nom > second.last_nom)
return 1;
return 0;
}
objs.sort(compare);
As of 2018 there is a much shorter and elegant solution. Just use. Array.prototype.sort().
Example:
var items = [
{ name: 'Edward', value: 21 },
{ name: 'Sharpe', value: 37 },
{ name: 'And', value: 45 },
{ name: 'The', value: -12 },
{ name: 'Magnetic', value: 13 },
{ name: 'Zeros', value: 37 }
];
// sort by value
items.sort(function (a, b) {
return a.value - b.value;
});
I haven't seen this particular approach suggested, so here's a terse comparison method I like to use that works for both string and number:
const objs = [
{ first_nom: 'Lazslo', last_nom: 'Jamf' },
{ first_nom: 'Pig', last_nom: 'Bodine' },
{ first_nom: 'Pirate', last_nom: 'Prentice' }
];
const sortBy = fn => (a, b) => -(fn(a) < fn(b)) || +(fn(a) > fn(b))
const getLastName = o => o.last_nom
const sortByLastName = sortBy(getLastName)
objs.sort(sortByLastName)
console.log(objs.map(getLastName))Here's an explanation of sortBy():
sortBy() accepts a fn that selects what value from an object to use as comparison, and returns a function that can be passed directly to Array.prototype.sort(). In this example, we're using o.last_nom as the value for comparison, so whenever we receive two objects through Array.prototype.sort() such as
{ first_nom: 'Lazslo', last_nom: 'Jamf' }
and
{ first_nom: 'Pig', last_nom: 'Bodine' }
we use
(a, b) => -(fn(a) < fn(b)) || +(fn(a) > fn(b))
to compare them.
Remembering that fn = o => o.last_nom, we can expand the compare function to the equivalent
(a, b) => -(a.last_nom < b.last_nom) || +(a.last_nom > b.last_nom)
The logical OR || operator has a short-circuiting functionality that's very useful here. Because of how it works, the body of the function above means
if (a.last_nom < b.last_nom) return -1
return +(a.last_nom > b.last_nom)
So if a < b we return -1, otherwise if a > b then we return +1, but if a == b, then a < b and a > b are false, so it returns +0.
As an added bonus, here's the equivalent in ECMAScript 5.1 without arrow functions, which is unfortunately not quite as terse:
var objs = [
{ first_nom: 'Lazslo', last_nom: 'Jamf' },
{ first_nom: 'Pig', last_nom: 'Bodine' },
{ first_nom: 'Pirate', last_nom: 'Prentice' }
];
var sortBy = function (fn) {
return function (a, b) {
return -(fn(a) < fn(b)) || +(fn(a) > fn(b))
}
}
var getLastName = function (o) { return o.last_nom }
var sortByLastName = sortBy(getLastName)
objs.sort(sortByLastName)
console.log(objs.map(getLastName))</div>