逻辑运算符 || 在javascript中，0代表布尔假？

Question

I happened to know the following code

Here is the code, and very simple:

var test = 0 || -1 ;
console.log(test);

then the output in the console is -1

and somehow i am really new into the javascript,

all i think of is that the 0 stands for Boolean False in JS ,and so || operator seems to ignore the 0 and assign the value -1 to the variable

so am i right ? i just want a confirm

Answer 1

• || — expr1 || expr2 expr1 || expr2 (Logical OR)

  Returns expr1 if it can be converted to true; otherwise, returns expr2. Thus, when used with Boolean values, || returns true if either operand is true; if both are false, returns false..

• && — expr1 && expr2 (Logical AND)

  Returns expr1 if it can be converted to false; otherwise, returns expr2. Thus, when used with Boolean values, && returns true if both operands are true; otherwise, returns false.

All values in Javascript are either "truthy" or "falsy".
The following values are equivalent to false in conditional statements :

• false
• null
• undefined
• The empty string "" (\\ '' )
• The number 0
• The number NaN

All other values are equivalent to true.

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So... var test = 0 || -1 ; var test = 0 || -1 ; returns -1 .

If it was var test = 0 || false || undefined || "" || 2 || -1 var test = 0 || false || undefined || "" || 2 || -1 var test = 0 || false || undefined || "" || 2 || -1 it would return 2

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Logical operator on MDN

Answer 2

You can use Nullish coalescing operator (??)

The nullish coalescing operator (??) is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.

Only null and undefined will be falsey. 0 will be considered true. But take care: an empty string will be considered true too!

 console.log('0 ?? 1 ->', 0 ?? 1) // expected output: 0 console.log('null ?? 1 -> ', null ?? 1) // expected output: 1 console.log('undefined ?? 1 ->', undefined ?? 1) // expected output: 1 console.log('"" ?? 1 ->', "" ?? 1) // expected output: ""