//写法三,用.trim().length来判断(符合预期,trim后长度都为0)console.log("写法三,用.trim().length来判断");if(addr.trim().length > 0) { console.log("addr有值,不为empty"); }else{ console.log("trim后长度为:" +addr.trim().length); console.log("addr没值,empty"); }if(billAddr.tri...
function isEmpty(obj) { for(var prop in obj) { if(obj.hasOwnProperty(prop)) return false; } return true; } In the above code, we will loop through object properties and if an object has at least one property, then it will enter the loop and return false. If the object doesn’t...
if (isEmpty(s)) { alert("输入的E-mail地址不能为空,请输入!"); return false; } //is s contain whitespace if (isWhitespace(s)) { alert("输入的E-mail地址中不能包含空格符,请重新输入!"); return false; } var i = 1; var len = s.length; if (len > 40) { alert("E-mail地址长...
letvalue;value// 👈 null and undefined check&&Object.keys(value).length===0&&value.constructor===Object;value=null;// nullvalue=undefined;// undefined Perfect, no error is thrown 😁 #B. Empty Object Check in Older Browsers What if you need to support older browsers? Heck, who am I...
This was used frequently until the JavaScript ES5 era, when there were no built-in methods available to check if an object is empty. Let’s go through the following example. 1 function isEmptyObject(obj) { 2 for (var property in obj) { 3 if (obj.hasOwnProperty(property)) { 4 ...
It is most commonly used in combination with aternary operatorto set a default as certain variable has not been initialized : var dark = typeof darkColor !== typeof undefined ? darkColor : "black"; Related Searches to JavaScript check if variable exists (is defined/initialized) - javascript...
2. 简化 if true...else 对于不包含大逻辑的 if-else 条件,可以使用下面的快捷写法。我们可以简单地使用三元运算符来实现这种简化。 如果有嵌套的条件,可以这么做。 3. if 判断值是否存在 这是我们都在使用的一种常用的简便技巧,在这里仍然值得再提一下。
// Define the original function.var checkNumericRange = function (value) { if (typeof value !== 'number') return false; else return value >= this.minimum && value <= this.maximum;}// The range object will become the this value in the callback function.var range = { minimum: 10, ...
alert("is null"); } 1. 2. 3. 4. 5. 为了向下兼容,exp 为 null 时,typeof null 总返回 object,所以不能这样判断。 代码如下: var exp = null; if (isNull(exp)) { alert("is null"); } 1. 2. 3. 4. 5. 判断字符串是否为空 ...
C: "Lydia" ["", " is ", " years old"] 21 答案: B 如果使用标记模板字面量,第一个参数的值总是包含字符串的数组。其余的参数获取的是传递的表达式的值! 18. 输出是什么? function checkAge(data) { if (data === { age: 18 }) { console.log('You are an adult!') } else if (data...