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JS |真與假|

王林
王林原創
2024-09-01 21:05:36507瀏覽

Js | Truthy & Falsy |

真值與假值:

在 Javascript 中,真值和假值用來決定布林值中的值是 true 或 false
context.這個概念對於使用 if 語句等條件控製程式流程至關重要。

Falsy Values: 0," ",null,NaN,false,undefined 
console.log(Boolean(0)); //false
console.log(Boolean(undefined)); //false

console.log(Boolean(' '));  //empty false

console.log(Boolean(null)); //false

console.log(Boolean(NaN)); //false not a number

console.log(Boolean(false)); //false

真值:任何非假值:

console.log(Boolean(1)); //true
console.log(Boolean(1833933)); //true
console.log(Boolean(-1)); //true
console.log(Boolean("hello")); //true
console.log(Boolean(1)); //true
console.log(Boolean([])); //true empty array
console.log(Boolean({})); //true empty object
console.log(function (){}); //true
Example:
           t     f
let cash =255  //0 ; 
    //conditions false  statement block not run
if (cash){
  console.log("you can buy burger with drink"); 
}else{
   console.log("you can buy burger"); 
}else{
   console.log("you don't have money"); 
}
let a;
console.log(a); //false
output:
undefined 
let a = 10;
console.log(a); //true
let a = null;
console.log(a); //false

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