~~~ for (var i = 0; i < 10; i++) { console.log(i); //=>0 break; } console.log(i); //=>0 for (var i = 0; i < 10; i++) { continue; //=>结束本轮循环（循环体中continue下面代码不在执行，继续累加执行下一轮） console.log(i); } console.log(i); //=>10 for (var i = 1; i <= 10; i += 2) { if (i <= 5) { i++; continue; } else { i -= 2; break; } i--; console.log(i); } console.log(i); //=>5 // 造成了死循环：一直在加载，什么都不输出 for (var i = 3; i < 12; i++) { if (i < 3) { i++; break; } if (i > 9) { i += 2; continue; } i--; } console.log(i); ~~~ ~~~ // 条件?成立:不成立; let a = 12; if (a >= 0 && a <= 20) { if (a % 2 === 0) { a += 2; } } else { a -= 2; } a >= 0 && a <= 20 ? (a % 2 === 0 ? a += 2 : null) : a -= 2; console.log(a); //=>14 ~~~ ~~~ let a = typeof typeof typeof [12,23]; ~~~ ~~~ let a = typeof typeof typeof [12,23]; console.log(a); ~~~  ~~~ // == 比较的时候，如果左右两边数据类型不一致则先转换为相同的类型，再比较 '10' == 10 TRUE let a = '10'; a == 10 ? a++ : a--; console.log(a);//11 /* * a++ 和 a+=1 和 a=a+1 都是在自身基础上累加1，但是a++浏览器会给其做特殊处理（会把其转换为数字再进行累加） * a++ => a=Number(a)+1 * a+=1 => a=a+1 */ let b = '10'; switch (b) { case 10: //=>每一种case都是===进行比较的 '10'===10 FALSE b++; break; default: b--; } console.log(b); //=>9 ~~~   ``` !(!"Number(undefined)"); /* * "" '' `` 都是字符串 => "Number(undefined)"就是一个字符串 * !"Number(undefined)" 转换为布尔在取反 => false * !false => true */ //0 NaN null undefined 空字符串是false isNaN(parseInt(new Date())) + Number([1]) + typeof undefined;​ /* * + 是最后计算的，先把每一项的值都算出来，最后相加 * isNaN(parseInt(new Date())) 从最里层开始逐一向外层计算 * new Date() => 当前本机日期（对象） * parseInt(对象) => parseInt("Fri Mar 06 2020 11:43:18 GMT+0800") =>NaN * isNaN(NaN) => true * Number([1]) * Number("1") =>1 * typeof undefined * =>"undefined" * true + 1 + "undefined" * true + 1 => 2 * 2 + "undefined" => "2undefined" */ Boolean(Number("")) + !isNaN(Number(null)) + Boolean("parseInt([])") + typeof !(null);​ /* * Boolean(Number("")) * Number("") => 0 * Boolean(0) => false * !isNaN(Number(null)) * Number(null) => 0 * isNaN(0) => false * !false => true * Boolean("parseInt([])") * "parseInt([])" 他是一个字符串，并不是转换数字啥的 * => true * typeof !(null) * !(null) => true * typeof true => "boolean" * false + true + true + "boolean" => "2boolean" */ parseFloat("1.6px") + parseInt("1.2px") + typeof parseInt(null);​ /* * parseFloat("1.6px") => 1.6 * parseInt("1.2px") => 1 * typeof parseInt(null) * parseInt(null) => parseInt('null') => NaN * typeof NaN => "number" * 1.6 + 1 + "number" => '2.6number' */ isNaN(Number(!!Number(parseInt("0.8"))));​ /* * parseInt("0.8") => 0 * !!Number(0) => false * Number(false) => 0 * isNaN(0) => false */ console.log(1 + "2" + "2");​ /* * '122' */ !typeof parseFloat("0");​ /* * parseFloat("0") => 0 * typeof 0 => "number" * !"number" => false */ Number("");​ /* 0 */ typeof "parseInt(null)" + 12 + !!Number(NaN);​ /* * typeof "parseInt(null)" => "string" * 12 * !!Number(NaN) => false * => "string12false" */ Number(NaN) //NaN !NaN //true !typeof (isNaN("")) + parseInt(NaN);​ /* * !typeof (isNaN("")) * isNaN("") => isNaN(Number("")) => isNaN(0) => false * typeof false => "boolean" * !"boolean" => false * parseInt(NaN) * parseInt(String(NaN)) => parseInt('NaN') => NaN * false + NaN => NaN */ typeof !parseInt(null) + !isNaN(null); /* * typeof !parseInt(null) * parseInt(null) => parseInt('null') => NaN * !NaN => true * typeof true => "boolean" * !isNaN(null) * isNaN(null) => isNaN(Number(null)) => isNaN(0) => false * !false => true * "boolean" + true => "booleantrue" */ ```