This way will evaluate to true when myVar is null, but it will also get executed when myVar is any of these:. There may be many shortcomings, please advise. From Mozilla's documentation: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined, I see this: One reason to use typeof() is that it does not throw an error if the variable has not been defined. NULL doesn't exist, but may at best be an alias for null, making that a redundant or broken condition. JavaScript Null Check: How Does It Work? - /* Position Is Everything If an object property hasn't been defined, an error won't be thrown if you try and access it. . How to check if a Variable Is Not Null in JavaScript - GeeksforGeeks How to get the first non-null/undefined argument in JavaScript 0 and false, using if(obj.undefProp) is ok. By using our site, you 2968 Is there a standard function to check for null, undefined, or blank variables in JavaScript? Hide elements in HTML using display property. So in this situation you could shorten: With this in mind, and the fact that global variables are accessible as properties of the global object (window in the case of a browser), you can use the following for global variables: In local scopes, it always useful to make sure variables are declared at the top of your code block, this will save on recurring uses of typeof. Stop Googling Git commands and actually learn it! Caveat emptor :), Best way to compare undefined or null or 0 with ES5 and ES6 standards, _.isNil(value) gives true for both null and undefined. }. Oh, now I got what you mean; your comment is misleading because was looking like related to the correctness of the code. The variable is neither undefined nor null Also, like the typeof approach, this technique can "detect" undeclared variables: But both these techniques leak in their abstraction. As @CMS pointed out, this has been patched in ECMAScript 5th ed., and undefined is non-writable. Well, not an empty array, but an empty object, and yes that would be expected.
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