JS: About logic operation

A, logical operators

　　Logical operators for determining the logical connection between the variable or value.

　　

 

　　example:

　　2 = 1 &&> 2 when the first value may be converted to true returns the second value; otherwise, it returns a first value;

　　2 || 0 => 2 when the first value may be converted to a value of true is returned; otherwise, it returns the second value;

　　As well as when we write the callback function, it is generally better to write:

function fn(callback){
    return callback && callback()
}

fn(function(){})

Second, the expression will be converted to false are:

• null;
• NaN;
• 0;
• Empty string ( '' || "" || ``);
• undefined;