how to run colease in javascript code example

Example 1: nullish coalesing

Expression:
	Left ?? Right
if left is null or undefined , then Right will be the value 

const a = '' ;
const b = undefined;

const c = a ?? 'default' ; // will give c =''
const d = b ?? 'default' ; // wil give d = 'default'

Example 2: nullish-coalescing-operator

null || undefined ?? "foo"; // raises a SyntaxError
true || undefined ?? "foo"; // raises a SyntaxError