None.

A new string representing str stripped of whitespace from its end (right side). Whitespace is defined as white space characters plus line terminators.

If the end of str has no whitespace, a new string is still returned (essentially a copy of str).

After trim() was standardized, engines also implemented the non-standard method trimRight. However, for consistency with padEnd(), when the method got standardized, its name was chosen as trimEnd. For web compatibility reasons, trimRight remains as an alias to trimEnd, and they refer to the exact same function object. In some engines this means:

String.prototype.trimRight.name === "trimEnd";

The following example trims whitespace from the end of str, but not from its start.

let str = "   foo  ";

console.log(str.length); // 8

str = str.trimEnd();
console.log(str.length); // 6
console.log(str); // '   foo'

• Polyfill of String.prototype.trimEnd in core-js
• String.prototype.trim()
• String.prototype.trimStart()