For example there is the fact that undefined will evaluate to false, and that the undefined value is just one of many other values that will do so. However there is much to be aware of when it comes to this value in javaScript, not just with the value itself, but of course with many things in core javaScript that branch off from it. So chances are if you have been fiddling with javaScript for at least a little while, are you have come across undefined a few times all ready.
That is that I often find myself using the undefined keyword as a way to test for undefined by combining the undefined keyword with an identity operator and a value that is to be tested for undefined. There is also the undefined keyword that can be used to intentionally set a variable to undefined, and can also be used in expressions when it comes to testing for undefined. Still it might be a good idea to have the function return false anyway just for the sake of making things explicit. This might be a good thing in some cases as undefined will evaluate to false, so when it comes to functions that return a boolean value it might not always present a problem. When working with functions a value of undefined is what is returned by a function by default unless something else is returned by using the return keyword. This can often be the case when choosing to go with function expressions rather than declarations and neglect to do what is required to keep that from happening, or it could just be a simple typo. If I attempt to call an object property that I expect is a function, but turns out to be undefined, that can result in an Error that is the result of calling undefined. However an object key and a variable can be both declared, and intensionally assigned the value undefined bu using the undefined keyword, or preforming any kind of action that will result in the value of undefined being set to the variable or object property. In addition if I attempt to access an object property value that is not defined, then the result is undefined. For one thing the undefined value is the default value for variables that are declared, but do not have any value assigned to them. If you have done more than one day’s programming in any language you will realise that this is an important building block for programmers.In javaScript undefined is a value that comes up often when working with various code examples, and projects. Undefined is a JavaScript primitive that is used when a value has not been assigned a value. Last updated Wednesday, The void of undefined in JavaScript You can't trust undefined in JavaScript even after ES5 made it immutableĮstimated reading time: 3 minutes Table of contents
The void of undefined in JavaScript | George Ornbo
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