What happens when a function is assigned to a variable in javascript?
Here's the rundown on the standard forms that create functions: (Originally written for another question, but adapted after being moved into the canonical question.) Show
Terms:
The quick list:
Function DeclarationThe first form is a function declaration, which looks like this:
A function declaration is a declaration; it's not a statement or expression. As such, you don't follow it with a
A function declaration is processed when execution enters the context in which it appears, before any step-by-step code is executed. The function it creates is given a proper name ( Because it's processed before any step-by-step code in the same context, you can do things like this:
Until ES2015, the spec
didn't cover what a JavaScript engine should do if you put a function declaration inside a control structure like
And since they're processed before step-by-step code is run, it's tricky to know what to do when they're in a control structure. Although doing this wasn't specified until ES2015, it was an allowable extension to support function declarations in blocks. Unfortunately (and inevitably), different engines did different things. As of ES2015, the specification says what to do. In fact, it gives three separate things to do:
The rules for the loose modes are tricky, but in strict mode, function declarations in blocks are easy: They're local to the block (they have block scope, which is also new in ES2015), and they're hoisted to the top of the block. So:
"Anonymous" function ExpressionThe second common form is called an anonymous function expression:
Like all expressions, it's evaluated when it's reached in the step-by-step execution of the code. In ES5, the
function this creates has no name (it's anonymous). In ES2015, the function is assigned a name if possible by inferring it from context. In the example above, the name would be Named function ExpressionThe third form is a named function expression ("NFE"):
The function this creates has a proper name (
Note that NFEs have frequently been a source of bugs for JavaScript implementations. IE8 and earlier, for instance, handle NFEs completely incorrectly, creating two different functions at two different times. Early versions of Safari had issues as well. The good news is that current versions of browsers (IE9 and up, current Safari) don't have those issues any more. (But as of this writing, sadly, IE8 remains in widespread use, and so using NFEs with code for the web in general is still problematic.) Accessor Function Initializer (ES5+)Sometimes functions can sneak in largely unnoticed; that's the case with accessor functions. Here's an example:
Note that when I used the function, I didn't use You can also create accessor functions
with Arrow Function Expression (ES2015+)ES2015 brings us the arrow function. Here's one example:
See that A couple of things about arrow functions:
The
(Remember that In
both cases, the body of the function is just an expression; the function's return value will automatically be the result of that expression (you don't use an explicit If you're doing more than just a single expression, use
The version without Method Declaration in Object Initializer (ES2015+)ES2015 allows a shorter form of declaring a property that references a function called a method definition; it looks like this:
the almost-equivalent in ES5 and earlier would be:
the difference (other than verbosity) is that a method can use That also means that the method has a reference to the object it was defined on, so if that object is temporary (for instance, you're passing it into Constructor and Method Declarations in class (ES2015+)ES2015 brings us
There are two function declarations above: One for the constructor, which gets the name Can a function be assigned to a variable in JavaScript?It is possible to use a function expression and assign it to a regular variable, e.g. const factorial = function(n) {...} .
What happens when you assign a function to a variable?In Python, we can assign a function to a variable. And using that variable we can call the function as many as times we want. Thereby, increasing code reusability. Simply assign a function to the desired variable but without () i.e. just with the name of the function.
What happens when a function is called in JavaScript?Invoking a JavaScript Function
The code inside a function is not executed when the function is defined. The code inside a function is executed when the function is invoked. It is common to use the term "call a function" instead of "invoke a function".
How do you call a function stored in a variable in JavaScript?There are two methods to call a function from string stored in a variable. The first one is by using the window object method and the second one is by using eval() method. The eval() method is older and it is deprecated.
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