How to add an array of key value pairs to a Map in JavaScript? - Stack Overflow

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I have an array of key value pairs where each key has an another array of constant length (i.e., 2) as the value. How can I add the entire array to a Map() without just doing Map.set(key, value) for every pair?

I know that while creating a Map() instance I could pass an iterable like an array to it ex: let x = new Map(arr); But this is not supported in IE 11 as per the documentation here. So, could anyone help me out with an alternate implementation.

At the end of the day, I just want to be able to access the two values with a string key. If there is an another way I could implement, please guide me.

Here is the example:

I created a key value mapping array as follows:

let arr = [
        ['ar', ['cl', 'bl']],
        ['bs', ['kl', 'ml']],
        ['cs', ['rk', 'uk']],
        ['da', ['mk', 'ak']]
    ];
let map = new Map(arr); // This isn't working. 

Thank you.

I have an array of key value pairs where each key has an another array of constant length (i.e., 2) as the value. How can I add the entire array to a Map() without just doing Map.set(key, value) for every pair?

I know that while creating a Map() instance I could pass an iterable like an array to it ex: let x = new Map(arr); But this is not supported in IE 11 as per the documentation here. So, could anyone help me out with an alternate implementation.

At the end of the day, I just want to be able to access the two values with a string key. If there is an another way I could implement, please guide me.

Here is the example:

I created a key value mapping array as follows:

let arr = [
        ['ar', ['cl', 'bl']],
        ['bs', ['kl', 'ml']],
        ['cs', ['rk', 'uk']],
        ['da', ['mk', 'ak']]
    ];
let map = new Map(arr); // This isn't working. 

Thank you.

• javascript
• arrays
• dictionary

Share Improve this question Follow edited Feb 2, 2018 at 15:32 Tums asked Feb 2, 2018 at 15:07 TumsTums 58922 gold badges66 silver badges1616 bronze badges 0

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 5

If you need to support browsers where the Map is not implemented, just use ordinary object, where the 1st array item will be keys & 2nd (the sub-array) values:

var arr = [
        ['ar', ['cl', 'bl']],
        ['bs', ['kl', 'ml']],
        ['cs', ['rk', 'uk']],
        ['da', ['mk', 'ak']]
    ];

var map = arr.reduce(function (obj, item) {
    obj[item[0]] = item[1];
    return obj;
}, {});

console.log(map['ar'], map.bs);

Or ES2015 approach (won't work in IE11):

const map = arr.reduce((obj, item) => ({
    ...obj,
    [item[0]]: item[1],
}), {});

If you want to access the subarray by the string key, you'd have to convert it from array anyways.

If you'd want to use Map, then (apart from fixing typos in your array definition) you'll extract the contents by Map.prototype.get function:

var map = new Map(arr);
console.log(map.get('bs'));

If you don't want to create a new object, another approach could be using Array.filter:

arr.filter(function (item) { return item[0] === 'ar' })[0][1];
arr.filter((item) => item[0] === 'ar')[0][1]; // ES2015

(potentially wrapped in a function)

You can use a object

let obj = 
{ ar:['cl', 'bl'],
  bs:['kl', 'ml'],
  cs:['rk', 'uk'],
  da:['mk', 'ak']
};
console.log(obj['bs'][1]); // displays 'ml'

I have an array of key value pairs where each key has an another array of constant length (i.e., 2) as the value. How can I add the entire array to a Map() without just doing Map.set(key, value) for every pair?

I know that while creating a Map() instance I could pass an iterable like an array to it ex: let x = new Map(arr); But this is not supported in IE 11 as per the documentation here. So, could anyone help me out with an alternate implementation.

At the end of the day, I just want to be able to access the two values with a string key. If there is an another way I could implement, please guide me.

Here is the example:

I created a key value mapping array as follows:

let arr = [
        ['ar', ['cl', 'bl']],
        ['bs', ['kl', 'ml']],
        ['cs', ['rk', 'uk']],
        ['da', ['mk', 'ak']]
    ];
let map = new Map(arr); // This isn't working. 

Thank you.

I have an array of key value pairs where each key has an another array of constant length (i.e., 2) as the value. How can I add the entire array to a Map() without just doing Map.set(key, value) for every pair?

I know that while creating a Map() instance I could pass an iterable like an array to it ex: let x = new Map(arr); But this is not supported in IE 11 as per the documentation here. So, could anyone help me out with an alternate implementation.

At the end of the day, I just want to be able to access the two values with a string key. If there is an another way I could implement, please guide me.

Here is the example:

I created a key value mapping array as follows:

let arr = [
        ['ar', ['cl', 'bl']],
        ['bs', ['kl', 'ml']],
        ['cs', ['rk', 'uk']],
        ['da', ['mk', 'ak']]
    ];
let map = new Map(arr); // This isn't working. 

Thank you.

• javascript
• arrays
• dictionary

Share Improve this question Follow edited Feb 2, 2018 at 15:32 Tums asked Feb 2, 2018 at 15:07 TumsTums 58922 gold badges66 silver badges1616 bronze badges 0

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 5

If you need to support browsers where the Map is not implemented, just use ordinary object, where the 1st array item will be keys & 2nd (the sub-array) values:

var arr = [
        ['ar', ['cl', 'bl']],
        ['bs', ['kl', 'ml']],
        ['cs', ['rk', 'uk']],
        ['da', ['mk', 'ak']]
    ];

var map = arr.reduce(function (obj, item) {
    obj[item[0]] = item[1];
    return obj;
}, {});

console.log(map['ar'], map.bs);

Or ES2015 approach (won't work in IE11):

const map = arr.reduce((obj, item) => ({
    ...obj,
    [item[0]]: item[1],
}), {});

If you want to access the subarray by the string key, you'd have to convert it from array anyways.

If you'd want to use Map, then (apart from fixing typos in your array definition) you'll extract the contents by Map.prototype.get function:

var map = new Map(arr);
console.log(map.get('bs'));

If you don't want to create a new object, another approach could be using Array.filter:

arr.filter(function (item) { return item[0] === 'ar' })[0][1];
arr.filter((item) => item[0] === 'ar')[0][1]; // ES2015

(potentially wrapped in a function)

You can use a object

let obj = 
{ ar:['cl', 'bl'],
  bs:['kl', 'ml'],
  cs:['rk', 'uk'],
  da:['mk', 'ak']
};
console.log(obj['bs'][1]); // displays 'ml'

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