functions
A function is seen as a wrapper to a block of code that is given a name. They can be executed from other areas of the program using the name.
We can define functions using the function keyword :
function hello(){
alert("Hello");
}
The above code creates a function named hello.
We can invoke this function as
hello();
JavaScript function arguments
When defining a function, we can provide names for arguments that are to be passed to it.
function hello(name) {
alert("Hello " + name);
}
We can call the function hello() with parameter “John” as :
hello("John");
JavaScript functions do not check parameter types
There is no type checking involved with function parameters.
So, we can also call the hello() function with integer parameter as well :
hello(1);
JavaScript functions do not check number of parameters
Functions automatically have access to a variable called arguments. This is an array-like object that reflects every value passed to the function when the function is called.
So, the following function call is still valid :
hello("John","Doe");
Output:
Hello John
JavaScript functions can not have default parameters
In JavaScript, function parameters in JavaScript cannot be set with a default value.
If a function has an parameter that is not passed a value when the function is called, that parameter will have a value of undefined.
hello();
Output:
Hello undefined
To create default value-like functionality, add a default value assignment within the function:
function hello(name) {
if (typeof name == 'undefined') {
name = "Unknown";
}
return ("Hello " + name);
}
Returning values from a function
A function may return data to the statement that called it.
To get a function to return a value, we use the return keyword, followed by the value we want it to return:
For example,
function hello(name) {
return ("Hello " + name);
}
A return statement is always the final act of a function; nothing else is processed
after a function has returned.
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