In general, you need to determine true or false in the following statement structure

If branch statement While loop statement The second statement in for

Such as

if (boo) {
// do something
}

while (boo) {
// do something
}

There are six values in JavaScript that are false, and these six values are

false null undefined 0 “(empty string) NaN

Where false itself is Boolean, the other five are not.

All but these six are “true”, including objects, arrays, regex, functions, and so on. Note that ‘0’, ‘null’, ‘false’, {}, [] are also true values.

Although all six values are false, they are not all equal

console.log( false == null ) // false
console.log( false == undefined ) // false
console.log( false == 0 ) // true
console.log( false == '' ) // true
console.log( false == NaN ) // false

console.log( null == undefined ) // true
console.log( null == 0 ) // false
console.log( null == '' ) // false
console.log( null == NaN ) // false

console.log( undefined == 0) // false
console.log( undefined == '') // false
console.log( undefined == NaN) // false

console.log( 0 == '' ) // true
console.log( 0 == NaN ) // false

For ”==”, the following conclusions are drawn

In addition to comparing false to itself to true, false is also true to 0 Null is true only when compared to undefined, and undefined is true only when compared to null. There is no second In addition to being true compared to false, 0 has an empty string ” The empty string "" is going to compare to false to true, with the number 0