function lookup() { firstName = /\w+/i(); if (!firstName) window.alert (RegExp.input + "非法输入"); else { count=0; for (i=0;i 输入你的姓然后按回车键。 <FORM><INPUT TYPE:"TEXT" NAME="FirstName" onChange="lookup(this);"></FORM> </HTML> 1. 2. 3. 4. 5. 6. 7. g...
We can check whether the length of this array is 0 or higher - denoting whether any keys are present or not. If no keys are present, the object is empty: Object.keys(obj).length === 0 && obj.constructor === Object; Note: The constructor check makes sure the passed argument is ...
In your day-to-day JavaScript development, you might need to check if an object is empty or not. And if you’ve had to do this, you probably know that there’s no single direct solution. However, there are different techniques that you can use to create a custom solution for your own...
// then run the following block.if (!argument) { return 'The argument is empty'} else { return 'The argument is not empty'} // Let's convert the previous block to a positive check const argument = null if (argument) { return 'The argument is present'} else { return 'The argument...
error: Uncaught ReferenceError: somevariable is not defined Note:This isn't to say thattypeofis inherently a bad choice - but it does entail this implication as well. Using Lodash to Check if Variable isnull,undefinedornil Finally - you may opt to choose external libraries besides the built...
Last week, I shared how tocheck if an input is empty with CSS. Today, let’s talk about the same thing, but with JavaScript. It’s much simpler. Here’s what we’re building: Events to validate the input If you want to validate the input when a user types into the field, you ca...
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。
if(x.trim() =="")throw"is empty"; if(isNaN(x))throw"is not a number"; x = Number(x); if(x >10)throw"is too high"; if(x <5)throw"is too low"; } catch(err){ message.innerHTML="Error: "+ err +"."; } finally{ ...
In this tutorial, we are going to show you the ways of checking whether the JavaScript string is empty, undefined, or null. Just follow the guidelines.
function checkform(theform){ if(theform.name.value==""){ alert("姓名不能为空!"); theform.name.focus(); return false; } if(theform.tel.value==""){ alert("电话不能为空!"); theform.tel.focus(); return false; } } </SCRIPT> ...