CODEWITHSUNDEEP
javascriptreactjsecmascript-6maps
Omkar
Omkar

Reputation: 2423

Callback function to store values in a Map in ES6

This question might have been asked before but I couldnt find answer after sufficiently searching for one.

I am working on a React app and I need to store the state which is a map in a local variable.

Following is my code which takes the component state and stores it in blockMap:

let blockMap = this.state.editorState.getCurrentContent().getBlockMap();

Then I declare a new Map:

let tempMap = new Map();

Now, I need to store values into the tempMap. So I do something like this:

blockMap.forEach((k,v) => tempMap.set(k,v));

And then I just print out the tempMap to see the set variables. Unfortunately, I get an empty map again. I just dont understand why this is happening. Can someone explain to me if its an ES6 issue or something else?

Following is the full function:

printMapOfEditorState(){
    let blockMap = this.state.editorState.getCurrentContent().getBlockMap();
    let map = this.state.map;
    let tempMap = new Map();
    blockMap.forEach((k,v) => tempMap.set(k,v));
    console.log(tempMap);
}

Just one more follow up, in the same function I change the map state by using setState like this:

blockMap.forEach(k => {
    if(k.getText().replace(/^\s+|\s+$/g, '') !== undefined) {
        this.setState({
            map: map.set(k.getText(), k.getDepth())
        });
    }
});

And surprisingly this works. I cant understand this anomolous behaviour. Thanks for help.

Upvotes: 1

Views: 57

Answers (1)

FuzzyTree
FuzzyTree

Reputation: 32392

The arguments to the callback to forEach take the form of (value, key) as opposed to (key, value), so your forEach should look like

blockMap.forEach((v,k) => tempMap.set(k,v));
                  ^^^ swapped

But you actually don't need a forEach since Map can take another map in the constructor:

let tempMap = new Map(blockMap);

Upvotes: 1

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