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