Boolean API
1. Convert to Booleans
Boolean(value)
Boolean(expression)
mynote: Boolean() 的參數可以分 2 種類型:
- 如果只放 一個值 ,表示判斷 是否有值
- 如果放的是 一個式子 , 表示 普通的布林判斷式評算
Basic Example:
console.log( Boolean(-1) ); //true
console.log( Boolean(10>9) ); //true
console.log( (10>9) ); //true
When 放一個值:How Boolean() works?
- Everything With a "Value" is True
- Everything Without a "Value" is False
// With Value (true)
console.log( Boolean(10) );
console.log( Boolean(-1) );
console.log( Boolean("false") );
console.log( Boolean(true) );
console.log( Boolean(new Date()) );
// Without Value (false)
console.log( Boolean() );
console.log( Boolean(0) );
console.log( Boolean(-0) );
console.log( Boolean('') );
console.log( Boolean(NaN) );
console.log( Boolean(undefined) );
console.log( Boolean(null) );
console.log( Boolean(false) );
When 放一個式子:How Boolean() works?
- 根據布林運算子的規則進行評算
// Comparision Evaluation
console.log( Boolean( false == 0 ) ); //true
console.log( Boolean( false === 0 ) ); //false
console.log( Boolean( true == 1 ) ); //true
console.log( Boolean( true == 2) ); //false
console.log( Boolean( true === 1 ) ); //false
console.log( Boolean( null == 0) ); //false
console.log( Boolean( null == undefined ) ); //true
console.log( Boolean( null === undefined ) ); //false
console.log( Boolean( undefined == 0 ) ); //false
console.log( Boolean( 'John' > null ) ); //false
console.log( Boolean( 1 > null ) ); //true
console.log( Boolean( 0 > null ) ); //false
console.log( Boolean( 1 > NaN ) ); //false
When 放多個參數:How Boolean() works?
- 似乎以第一個參數的 Boolean() 結果為準
console.log( Boolean('John', 1>2) ); //true
console.log( Boolean(10>9, 1>2) ); //true
console.log( Boolean(1>2, 10>9) ); //false