The Boolean() constructor is used to create Boolean objects.

Syntax

new Boolean([value])

Parameters

value Optional

The initial value of the Boolean object.

Creating Boolean objects with an initial value of false

let bNoParam = new Boolean();
let bZero = new Boolean(0);
let bNull = new Boolean(null);
let bEmptyString = new Boolean('');
let bfalse = new Boolean(false);

Creating Boolean objects with an initial value of true

let btrue = new Boolean(true);
let btrueString = new Boolean('true');
let bfalseString = new Boolean('false');
let bSuLin = new Boolean('Su Lin');
let bArrayProto = new Boolean([]);
let bObjProto = new Boolean({});

Array.prototype.every()

The every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.

The every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.

Syntax

arr.every(callback(element[, index[, array]])[, thisArg])

Parameters

callback

A function to test for each element, taking three arguments:

element

The current element being processed in the array.

index Optional

The index of the current element being processed in the array.

array Optional

The array every was called upon.

thisArg Optional

A value to use as this when executing callback.

Return value

true if the callback function returns a [truthy]

value for all elements, every returns true.

Caution: Calling this method on an empty array will return true for any condition!

callback is invoked only for array indexes which have assigned values. It is not invoked for indexes which have been deleted, or which have never been assigned values.

callback is invoked with three arguments: the value of the element, the index of the element, and the Array object being traversed.

If a thisArg parameter is provided to every, it will be used as callback’s this value. Otherwise, the value undefined will be used as its this value. The this value ultimately observable by callback is determined according to the usual rules for determining the this seen by a function.

every acts like the “for all” quantifier in mathematics. In particular, for an empty array, it returns true.