We are frequently using the following code pattern in our JavaScript code if (typeof(some_variable) != ‘undefined’ && some_variable != null) { // Do something with some_variable } Is there a less verbose way of checking that has the same effect? According to some forums and literature saying simply the following should have the same effect. … Read more
How do I check a variable if it’s null or undefined and what is the difference between the null and undefined? What is the difference between == and === (it’s hard to search Google for “===” )? 8 s 8 How do I check a variable if it’s null or undefined… Is the variable null: … Read more
I have a global variable in JavaScript (actually a window property, but I don’t think it matters) which was already populated by a previous script, but I don’t want another script that will run later to see its value or that it was even defined. I’ve put some_var = undefined and it works for the … Read more
Why is null considered an object in JavaScript? Is checking if ( object == null ) Do something the same as if ( !object ) Do something ? And also: What is the difference between null and undefined? 22 s 22 (name is undefined) You: What is name? (*) JavaScript: name? What’s a name? I … Read more
I wanted to check whether the variable is defined or not. For example, the following throws a not-defined error alert( x ); How can I catch this error? 15 s 15 In JavaScript, null is an object. There’s another value for things that don’t exist, undefined. The DOM returns null for almost all cases where … Read more
I want to know what the difference is between null and undefined in JavaScript. 3 36
Which method of checking if a variable has been initialized is better/correct? (Assuming the variable could hold anything (string, int, object, function, etc.)) if (elem) { // or !elem or if (typeof elem !== ‘undefined’) { or if (elem != null) { 3 31
How do I determine if variable is undefined or null? My code is as follows: var EmpName = $(“div#esd-names div#name”).attr(‘class’); if(EmpName == ‘undefined’){ // DO SOMETHING }; <div id=”esd-names”> <div id=”name”></div> </div> But if I do this, the JavaScript interpreter halts execution. 3 33
Is there a universal JavaScript function that checks that a variable has a value and ensures that it’s not undefined or null? I’ve got this code, but I’m not sure if it covers all cases: function isEmpty(val){ return (val === undefined || val == null || val.length <= 0) ? true : false; } 4 … Read more
This question already has answers here: Detecting an undefined object property (50 answers) How to check a not-defined variable in JavaScript (15 answers) How to handle ‘undefined’ in JavaScript [duplicate] (3 answers) How can I check if a variable exist in JavaScript? (8 answers) Closed 7 years ago. What is the most appropriate way to … Read more
