理順 JavaScript (8) – 布爾相關問題

基本使用

var b;b = true;               alert(b);  //trueb = new Boolean(false); alert(b);  //falseb = 2 > 1;              alert(b);  //trueb = 2 

轉換到布爾

var b;b = Boolean(123);       alert(b); //trueb = Boolean('ABC');     alert(b); //trueb = Boolean(0);         alert(b); //falseb = Boolean('');        alert(b); //falseb = Boolean(NaN);       alert(b); //falseb = Boolean(null);      alert(b); //falseb = Boolean(undefined); alert(b); //falseb = Boolean(Infinity);  alert(b); //trueb = Boolean('false');   alert(b); //true

直接使用的自動轉換

var X;if (X) {alert('ok')} else {alert('no')};  //noX = 'ABC';if (X) {alert('ok')} else {alert('no')};  //okX = '';if (X) {alert('ok')} else {alert('no')};  //noX = -1;if (X) {alert('ok')} else {alert('no')};  //okX = 0;if (X) {alert('ok')} else {alert('no')};  //noX = new Date();if (X) {alert('ok')} else {alert('no')};  //ok

布爾運算

var b;b = !b;             alert(b); //falseb = !b;             alert(b); //trueb = true && true;   alert(b); //trueb = true && false;  alert(b); //falseb = false && true;  alert(b); //falseb = false && false; alert(b); //falseb = true || true;   alert(b); //trueb = true || false;  alert(b); //trueb = false || true;  alert(b); //trueb = false || false; alert(b); //false