JavaScript: Boolean Constructor
Boolean(arg)
-
Return
true
orfalse
, based on arg. new Boolean(arg)
- Return a Boolean object that represent true/false of arg.
When called as a function, it's used to convert a value to a boolean value, in the same way a “if” statement determines true/false.
// Boolean called as a function, returns true/false primitive value console.log( (typeof Boolean(3)) === "boolean" ); // true // Boolean called as a constructor, returns boolean object console.log( (typeof (new Boolean(3))) === "object" ); // true
Converting values to boolean.
// the following eval to false console.log( Boolean(0) ); // false console.log( Boolean(0.0) ); // false console.log( Boolean(0.) ); // false console.log( Boolean(.0) ); // false console.log( Boolean("") ); // false console.log( Boolean(null) ); // false console.log( Boolean(undefined) ); // false console.log( Boolean(NaN) ); // false // anything else is true console.log( Boolean(1) ); // true console.log( Boolean(-1) ); // true console.log( Boolean(Infinity) ); // true console.log( Boolean({}) ); // true console.log( Boolean([]) ); // true console.log( Boolean(function () {}) ); // true
Creating boolean object.
let xx = new Boolean(0); console.log( xx.valueOf() === false ); // true
Tip: the only practical use of Boolean()
is to force a value into true
or false
.
new Boolean(…)
is not very useful.