How do i pass a value from one function to another in javascript?
I am a beginner in JavaScript and wanted to ask the following: I have two simple functions and was wondering if there is any way to pass a variable value from one function to another. I know I can just move it outside the function to be used in other functions as well but just need to know the way how I can have one local variable and manipulate with it in my second function. Is this possible and how? Show
Here is some code:
The question is: how do I access variable
Chris 42.9k16 gold badges137 silver badges152 bronze badges asked May 14, 2012 at 8:20
3 First way is
// Then you will have to use this function for the variable1 so it doesn't really help much unless that's what you want to do. } Second way is
answered May 14, 2012 at 8:22
Pranay RanaPranay Rana 172k35 gold badges236 silver badges261 bronze badges 2 Adding to @pranay-rana's list: Third way is:
answered Feb 9, 2018 at 23:57
Asim MaharAsim Mahar 1,1801 gold badge9 silver badges13 bronze badges 1 You can very easily use this to re-use the value of the variable in another function.
Hassaan 6,8585 gold badges29 silver badges48 bronze badges answered Feb 1, 2016 at 9:36
Ankit JainAnkit Jain 2,2001 gold badge17 silver badges25 bronze badges learn how to pass functions as parameters in javascript. Functions are first-class citizens in the functional programming paradigm, which means they are just like variables. They can be passed as arguments to other functions, assigned to variables, and returned by other functions. This article explains how to pass functions as parameters in javascript in detail with examples. This article extensively discusses the following points: In functional programming, we assume functions to be ''first-class citizens''. By that, we mean that functions are treated as normal variables. They can be assigned values or passed to other functions as parameters, and functions can also return functions. How can we pass a variable to a function as its parameter? Let's first define a function that simply takes in a value and console it out. Now, we'll call this function and send a variable as an argument.
This code will obviously print 20 to the console. Sending functions to another function as arguments is also very similar. We'll see this in the next section. SyntaxNow, let us see how functions can be passed to another functions and how they can be used inside them. First, let us create a function that takes in a function and calls it inside its body.
And now, let's create another function that is to be called inside the calling function.
Now, let's call the function 'callingFunction' and pass the function 'functionToBeCalled' as its argument.
As you would have expected, the output of this code is: This is the function to be finally called! Now, let's understand this code.
Try console logging the parameter's value inside the callingFunction and see, I was not lying!
Common Examples of Callbacks
When we pass a function as an argument to another function, we call it callback. Callback simply means that the function will be called later! Why do we need Callbacks?
Note: The main goal of using callback functions is to handle the asynchronous nature of tasks. Consider this example: If we want to call function1 in case we get a response to the asynchronous function and call function2 if it encounters an error while performing that async task, we need callbacks here.
This is another simple example to explain where callbacks can be used.
These are two simple functions that print a message to the console. Now, let's create a function that will decide which function to be called based on the decision as to which out of A or B is actually greater.
Of course, the output is: A is smaller than B. We can see how functions can be easily passed as arguments to other functions just like regular variables and can be used inside the function bodies. This way, we say that these functions sent as arguments are callbacks. Some commonly used functions that take callbacks are parameters. Let's have a look at some of them:
Passing Functions without Invoking themHighlights: 1 - While passing callback, only pass the function's name and do not invoke the function. 2 - Understanding the correct syntax for passing a callback. Most people make a common mistake while passing functions as callbacks by invoking them. Remember, we always pass the function name to another function and do not call them while sending. The callback function actually gets called inside another function. Consider the following code snippet:
While passing the function 'function 'smile'', we called the function here itself by mistake.
See the output Window. We have the WRONG output. According to our code, function - smile shouldn't have been called because 23 > 45 is false. Also, This output is coming from the line no. 9, whereas we expect the smile function to be called at line no. 6. But, we have the smile statement on the console. Also, can you see the error - TypeError: smile is not a function? Let's understand this: When we pass the function name, we pass the reference to that function. The new function then has the reference to the original function. It can then call the function whenever it feels so, based on its decisions. But when we pass the invoked function, i.e., like this - func(). We are already calling the function. What we are passing to the next function is not the function reference but the output of our invoked function. This definitely cannot be called inside the next function's body. This is exactly what the error message is saying. The correct code for this logic is:
I hope you'll never make this mistake while working with callbacks. How to Pass Arguments Properly with Callbacks?Highlights: 1- Send callbacks by simply passing the function name 2 - Methods to pass callback functions with arguments Now, what if we need to pass some arguments to the callback function while it's being called inside the next function? One way of doing the same can be:
Clearly, the callback function is being invoked while being passed as an argument. We just learned this is the wrong way of passing callback functions. Then, how do we send arguments the right way? Now, see this:
Can I do this? Definitely yes! I'm sending a reference to a function, which is not a problem because I'm not invoking it. And that function calls smile along with the arguments. A short-hand notation of writing the same is:
This works as well because we are creating an anonymous function and passing it to another function.
Getting ‘‘this’’ Right when Passing FunctionsHighlights: 1 - this takes up the value of the object, calling it. 2 - While passed as a callback, the function looks for a global value of this. 3 - Steps to resolve this issue and bind the value of this are discussed Consider this code snippet:
''student'' is a simple object with one data variable, called ''name'' and a data function, named ''sayHi''. Inside the function ''sayHi'', ''this'' keyword refers to the object which called this data function. Here, ''this.name'' refers to the value of the name attribute of the object calling ''sayHi'', which is ''Rohit''. Output -
The CatchNow, what if I want to pass the function ''sayHi'' to another function as a callback. Will it still pick the correct value of ''this''? Let's try doing the same: It doesn't pick ''Rohit'' as the value of ''this.name''. Now, why is it so? When we pass a function as a callback, and that function uses the ''this'' keyword, it will start looking in the global context to find the value of ''this''. For this reason, we didn't get the value of ''this.name'' because in the global context, ''this'' doesn't exist in this code. We can solve this problem in two ways:
Let's discuss both in detail. Using 'bind' functionThe bind() function creates a bound function, which withholds the value of ''this'' within itself. For this reason, if we pass the function using ''this'' as a callback, that function will not look for global scope but will have the value of ''this'' bound to it. See the code and the output below. Here, the value of 'this.name' is rightly picked as 'Rohit'. This is because the function is now not looking at the global scope for the value of 'this'.
Creating an anonymous functionThis is another way to solve this issue. We can convert our function into an anonymous function. It gives us the correct result. Look at the console screenshot below. Conclusion
How can I access a variable value of a function from another function in JavaScript?function func1() { var num1 = 6; console. log(num1); } function func2() { var final = num1 + 5; console. log(final); } func2();
Can I pass object in function JavaScript?In JavaScript, you can use functions as values, just like numbers, strings, and objects. That means you can pass them as arguments, return them from other functions, and set them as properties of objects.
How do you pass a variable from one function to another in shell script?You have basically two options:. Make the variable an environment variable ( export TESTVARIABLE ) before executing the 2nd script.. Source the 2nd script, i.e. . test2.sh and it will run in the same shell.. |