CODEWITHSUNDEEP
javascriptarraysnode.js
user1939648
user1939648

Reputation:

Invalid array length when trying to create an array from calculation

var map = {
    mapSize: 100, // the size of a side
    data: new Array(this.mapSize * this.mapSize),

    getIndex: function(x, y) {
        return x * this.mapSize + y;
    },

    getCoords: function(index) {
        var x = Math.floor(index/this.mapSize);
        return {
            x: x,
            y: index - (x * this.mapSize)
        }
    }
};

This code gives me RangeError: Invalid array length.
However when there is no calculation, like this: 

data: new Array(this.mapSize),

it works.

Could you explain me why is that happening?

Upvotes: 1

Views: 2881

Answers (1)

dfsq
dfsq

Reputation: 193271

why is that happening

Because map object is not yet constructed by the time you are trying to read its mapSize property. So this.mapSize gives you undefined. As the result undefined * unedefined produces NaN. And Array can't be created with NaN length. Try just new Array(NaN) and you will see the same error.

Upvotes: 1

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