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  • What is the difference in JavaScript between undefined and not . . .
    Yes, variables can have a value of undefined and you can explicitly assign values to them Assigning undefined to a variable though is probably confusing, since it's a bit of a paradox (you've defined the variable as undefined) and it's not possible to distinguish that variable from either variables that don't exist or uninitialised variables
  • How can I check for undefined in JavaScript? - Stack Overflow
    – Daniel Schaffer Aug 2, 2010 at 18:09 3 See: How to check for undefined in javascript?, and whether a variable is undefined and How to handle ‘undefined’ in javascript – Shog9 Aug 3, 2010 at 8:47 3
  • What is the difference between null and undefined in JavaScript?
    The difference between null and undefined is: JavaScript will never set anything to null, that's usually what we do While we can set variables to undefined, we prefer null because it's not something that is ever done for us When you're debugging this means that anything set to null is of your own doing and not JavaScript
  • Javascript undefined condition - Stack Overflow
    undefined is a variable, not a constant, and can be assigned a value Because of this, one school of thought says the second path is safer, since you cannot be sure of the value of undefined There is another school of thought that says those who redefine undefined deserve exactly what they get
  • How to check for an undefined or null variable in JavaScript?
    If the purpose of the if statement is to check for null or undefined values before assigning a value to a variable, you can make use of the Nullish Coalescing Operator
  • How to handle undefined in JavaScript - Stack Overflow
    typeof foo !== 'undefined' window foo !== undefined 'foo' in window The first two should be equivalent (as long as foo isn't shadowed by a local variable), whereas the last one will return true if the global varible is defined, but not initialized (or explicitly set to undefined)
  • JavaScript checking for null vs. undefined and difference between . . .
    Example: x === null check whether it's undefined by either of two basic methods: direct comparison with undefined or typeof For various reasons, I prefer typeof x === "undefined" check whether it's one of null and undefined by using == and relying on the slightly arcane type coercion rules that mean x == null does exactly what you want
  • javascript - How to compare variables to undefined, if I don’t know . . .
    In JavaScript you can declare a variable and if it’s undefined, you can check variable == undefined; I know that, but how can you compare a value that you don’t know yet if it’s in memory? For exa


















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