CODEWITHSUNDEEP
javascript
Haslo Vardos
Haslo Vardos

Reputation: 322

Why [,,].join(' ') length is one less than array length?

What is the reason behind the length of string produced by joining var arr = [,,], like so: var str = arr.join(' ') being one less than length of arr.

var literal_arr = [,,],
    joined_literal_arr = literal_arr.join(' '),
    constructor_arr = new Array(2),
    joined_constructor_arr = new Array(2).join(' ');

console.log("Literal array notation length = ", literal_arr.length);

console.log("Joined literal array notation string length = ", joined_literal_arr.length);

console.log("Constructor array notation length = ", constructor_arr.length);

console.log("Joined constructor notation string length = ", joined_constructor_arr.length);

Upvotes: 1

Views: 1046

Answers (2)

Excalibur
Excalibur

Reputation: 367

It is simple as .join will join array elements with separator provided as argument. It won’t append separator after the last element or prepend it before the first element. It will place separator between elements only.

Upvotes: 0

Pranav C Balan
Pranav C Balan

Reputation: 115232

As per MDN docs :

If an element is undefined or null, it is converted to the empty string.

In your case, you are creating an array with a particular length without any value(it would be undefined). So while joining there will be length - 1 separators(since undefined already treated as an empty string) means length - 1 spaces(' ').

Upvotes: 5

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