Defining arrays in single line in Javascript

Question

I am trying to declare multiple arrays in a single line. But I am taking this error. (Cannot set property "0" of undefined)

var photos,tags = new Array();

flickrJSON.items.forEach(function(item, index) {
    photos[index] = item.media.m;
    tags[index] = item.tags;
});

Why I take this error? Can somebody explain? and How can I fix it

Just for the sake of interpreting the error, writing: var photos,tags = new Array(); is the same as writing var photos; var tags = new Array();. Hence the error (photos is undefined). — briosheje
– briosheje, Commented Nov 15, 2018 at 11:34

CertainPerformance · Accepted Answer · 2018-11-15 11:32:21Z

8

You're trying to use two arrays there - an array named photos, and an array named tags, so you need to use new Array (or, preferably, []) twice:

var photos = [], tags = [];

In your original code, var photos, will result in photos being undefined, no matter what comes after the comma.

If you wanted to create a lot of arrays at once and didn't want to repeat = [] each time, you could use Array.from with destructuring to keep code DRY:

const [arr1, arr2, arr3, arr4, arr5] = Array.from({ length: 5 }, () => []);

edited Nov 15, 2018 at 11:32

answered Nov 15, 2018 at 11:29

CertainPerformance

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omri_saadon · Accepted Answer · 2018-11-15 11:30:02Z

5

Using ES6 you can:

let [photos, tags] = [[], []];

answered Nov 15, 2018 at 11:30

omri_saadon

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