js creating map object

Question

I'm trying to create a map of objects to use by the following code:

var MARKED ={className: 'emoji', img:'⚐'} ;
var EMOJI_WONDER = {className: 'emoji', img: '🙄'};
var EMOJI_WIN = {className: 'emoji', img: '😁'};

var emoMap={};
emoMap[EMOJI_WONDER]=EMOJI_WONDER;
emoMap[MARKED]=MARKED;
emoMap[EMOJI_WIN]=EMOJI_WIN;
console.log(emoMap);

and i get object object. I've made a map before with the following code:

var str = 'this is a test la la la la lo';
var wordMap = countWordApperances(str);
console.log(str, 'got: ', wordMap);

function countWordApperances(txt) {
    var wordCountMap = {};
    
    var words = txt.split(' ');
    
    for (var i = 0; i < words.length; i++) {
        var currWord = words[i];
        if (wordCountMap[currWord]) wordCountMap[currWord]++;
        else wordCountMap[currWord] = 1;

    }
    return wordCountMap;
}

and i just can't tell why the top code won't set a map and the bottom code does.

T.J. Crowder · Accepted Answer · 2018-09-29 11:52:15Z

3

When you do this:

emoMap[EMOJI_WONDER]=EMOJI_WONDER;

you're using EMOJI_WONDER as both the key (name) of the property and its value. Property names can only be strings or Symbols, they cannot be objects. So when you do that, EMOJI_WONDER is coerced to string to form a property name. Since all of your objects are plain objects, they all coerce to the same string: "[object Object]". That's why your emoMap ends up with only one property.

Perhaps you meant to use the variable names as the property names:

emoMap.EMOJI_WONDER = EMOJI_WONDER;
// or
emoMap["EMOJI_WONDER"] = EMOJI_WONDER;

If not, you probably want an array or Set.

answered Sep 29, 2018 at 11:52

T.J. Crowder

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flyingfox · Accepted Answer · 2018-09-29 11:51:03Z

2

You have pass a variable object as a key for the object emoMap,you need to use string as key instead

var MARKED ={className: 'emoji', img:'⚐'} ;
var EMOJI_WONDER = {className: 'emoji', img: '🙄'};
var EMOJI_WIN = {className: 'emoji', img: '😁'};

var emoMap={};
emoMap["EMOJI_WONDER"]=EMOJI_WONDER;//add quote to make it work
emoMap["MARKED"]=MARKED;
emoMap["EMOJI_WIN"]=EMOJI_WIN;
console.log(emoMap);

answered Sep 29, 2018 at 11:51

flyingfox

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trk · Accepted Answer · 2018-09-29 12:01:31Z

0

What is happening in top case is that :

.toString() gets called and on MARKED, EMOJI_WONDER and EMOJI_WIN before using it as a key. Therefore, all assignments get loaded upon the same key. Viz: '[object Object]'.

Hence, when you print the output is:

{
    '[object Object]': {
        className: 'emoji',
        img: '😁'
    }
}

The final assignment (EMOJI_WIN)

answered Sep 29, 2018 at 12:01

trk

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