用JavaScript在单行中定义数组

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

Answer 1

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 }, () => []);

Answer 2

使用ES6，您可以：

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