How to create a string with n characters? How to create a string with specific length? [duplicate]

This is a forward-looking answer, and won’t work in current implementations.

ECMAScript 6 is currently defining a String.prototype.repeat method. This will allow you to do:

var result = "x".repeat(65535);

Again, this is a future addition. Currently ECMAScript 6 (Harmony) is being drafted, and this could technically be removed, though it doesn’t seem likely.

Current draft:

15.5.4.21 String.prototype.repeat (count)

The following steps are taken:

1. Let O be CheckObjectCoercible(this value).
2. Let S be ToString(O).
3. ReturnIfAbrupt(S).
4. Let n be the result of calling ToInteger(count).
5. ReturnIfAbrupt(n).
6. If n < 0, then throw a RangeError exception.
7. If n is +Infinity, then throw a RangeError exception.
8. Let T be a String value that is made from n copies of S appended together. If n is 0, T is the empty String.
9. Return T.

NOTE 1 This method creates a String consisting of the string elements of this object (converted to String) repeated
count time.

NOTE 2 The repeat function is intentionally generic; it does not require that its this value be a String object.Therefore, it can be transferred to other kinds of objects for use as a method.