How to create an associative array in JavaScript literal notation

问题

I understand that there are no associative arrays in JavaScript, only objects.

However I can create an array with string keys using bracket notation like this:

var myArray = [];
myArray['a'] = 200;
myArray['b'] = 300;
console.log(myArray); // Prints [a: 200, b: 300]

So I want to do the exact same thing without using bracket notation:

var myNewArray = [a: 200, b: 300]; // I am getting error - Unexpected token:

This does not work either:

var myNewArray = ['a': 200, 'b': 300]; // Same error. Why can I not create?

回答1:

JavaScript has no associative arrays, just objects. Even JavaScript arrays are basically just objects, just with the special thing that the property names are numbers (0,1,...).

So look at your code first:

var myArray = []; // Creating a new array object
myArray['a'] = 200; // Setting the attribute a to 200
myArray['b'] = 300; // Setting the attribute b to 300

It's important to understand that myArray['a'] = 200; is identical to myArray.a = 200;!

So to start with what you want: You can't create a JavaScript array and pass no number attributes to it in one statement.

But this is probably not what you need! Probably you just need a JavaScript object, what is basically the same as an associative array, dictionary, or map in other languages: It maps strings to values. And that can be done easily:

var myObj = {a: 200, b: 300};

But it's important to understand that this differs slightly from what you did. myObj instanceof Array will return false, because myObj is not an ancestor from Array in the prototype chain.

回答2:

You can use Map:

var arr = new Map([
   ['key1', 'User'],
   ['key2', 'Guest'],
   ['key3', 'Admin'],
]);

var res = arr.get('key2');
console.log(res); // The value is 'Guest'

回答3:

You want to use an object in this case

var myObject = {'a' : 200, 'b' : 300 };

This answer links to a more in-depth explanation: How to do associative array/hashing in JavaScript (http://blog.xkoder.com/2008/07/10/javascript-associative-arrays-demystified/)

回答4:

Arrays and Objects are different things.

For an object, you can do things like:

var obj = { "property1": "value1" };
obj.property2 = "value2";

For arrays, you have to do this:

var arr = [];
arr[0] = "value";

回答5:

Well, you are creating an array, which is in fact an object:

var arr = [];
arr.map;
// function(..)
arr['map'];
// function(..)

arr['a'] = 5;

console.log(arr instanceof Object); // true

You can add fields and functions to arr. It does not "insert" them into the array though (like arr.push(...)).

You can refer to an object fields with the [] syntax.

回答6:

You can do what you wanted to do this way:

myNewArray = new Array ({'a' : 200, 'b' : 300})

来源：https://stackoverflow.com/questions/37515959/how-to-create-an-associative-array-in-javascript-literal-notation

标签

javascript

arrays

associative-array