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javascriptarraysecmascript-6destructuring

ES6 nested array destructuring soft fail

How to manage the soft fail of the nested arrays in ES6?

Let's say we have a nested array with items and we want to get the first item:

const array = [[3,4,5,6]];
const [[firstItem]] = array; // firstItem = 3

console.log(firstItem);

I would like to protect against the situation when the array comes with a null, but apparently it doesn't work similarly to handling object soft fail:

const array = [null];
const [[firstItem] = []] = array; // Uncaught TypeError: array is not iterable

console.log(firstItem);

Solution

  • From destructuring assignment:

    Default values

    A variable can be assigned a default, in the case that the value unpacked from the array is undefined.

    You have null as value and not undefined.

    const array = [undefined];
const [[firstItem] = []] = array; // Uncaught TypeError: array is not iterable

console.log(firstItem);