JS-逻辑与、或、非

发表于2020年6月17日作者评心静气

与

var found = true;
var result = (found && someUndeclaredVariable);    // 直接报错
alert(result);    // 不会执行到此

var found = false;
var result = (found && someUndeclaredVariable); // 与上面相比，此处没错
alert(result);    //works

非

alert(!false);      //true
alert(!"blue");     //false
alert(!0);          //true
alert(!NaN);        //true
alert(!"");         //true
alert(!12345);      //false

alert(!!"blue");     //true
alert(!!0);          //false
alert(!!NaN);        //false
alert(!!"");         //false
alert(!!12345);      //true

或

var found = true;
var result = (found || someUndeclaredVariable);    //no error
alert(result);    //works

var found = false;
var result = (found || someUndeclaredVariable);    //error occurs here
alert(result);    //this line never executes