Possible Duplicate: Detecting an undefined object property in JavaScript javascript undefined compare How we can add a check for an undefined variable, like: function A(val) { if (val == undefined) // do this else // do this } 10 Answers 10
It’s difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 8 years ago. Locked. This question and its answers are locked … Read more
I’m trying to write a basic go program that calls a function on a different file, but a part of the same package. However, it returns: undefined: NewEmployee Here is the source code: main.go: package main func main() { emp := NewEmployee() } employee.go: package main type Employee struct { name string age int } … Read more
I’m checking if(response[0].title !== undefined), but I get the error: Uncaught TypeError: Cannot read property ‘title’ of undefined. 11 Answers 11
This question already has answers here: JavaScript check if variable exists (is defined/initialized) (31 answers) Closed 6 years ago. Things I’ve tried that don’t seem to work: if(lastName != “undefined”) if(lastName != undefined) if(undefined != lastName) 1 Answer 1
I know that I can test for a JavaScript variable and then define it if it is undefined, but is there not some way of saying var setVariable = localStorage.getItem(‘value’) || 0; seems like a much clearer way, and I’m pretty sure I’ve seen this in other languages. 13 Answers 13
I’m a bit confused about JavaScript’s undefined and null values. What does if (!testvar) actually do? Does it test for undefined and null or just undefined? Once a variable is defined can I clear it back to undefined (therefore deleting the variable)? Can I pass undefined as a parameter? E.g.: function test(var1, var2, var3) { … Read more
How do I verify the existence of an object in JavaScript? The following works: if (!null) alert(“GOT HERE”); But this throws an Error: if (!maybeObject) alert(“GOT HERE”); The Error: maybeObject is not defined. 18 Answers 18
The jQuery Core Style Guidelines suggest two different ways to check whether a variable is defined. Global Variables: typeof variable === “undefined” Local Variables: variable === undefined Properties: object.prop === undefined Why does jQuery use one approach for global variables and another for locals and properties? 8 Answers 8
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) { 31 Answers 31
