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Java script function
- 1. Presentation of java script Functions Functions are one of the fundamental building blocks in JavaScript. A function is a JavaScript procedure a set of statements that performs a task or calculates a value. The function define is a regular binding where the value of the binding is a function.
- 2. Defining a function A function is created with an expression that starts with the keyword function. Functions have set of parameters and body, which contains the statements that are to be executed when function is called. As in example below
- 3. Cont.. A function can have multiple parameter or no parameter at all. Parameters to a function behave like regular bindings, but their initial values are given by the caller of the function, not the code in the function itself.
- 4. Binding and scopes Each binding has a scope, which is the part of the program in which the binding is visible. For binding defined outside of any function or block, the scope is whole program is know as global binding. But binding created for function parameters of declared inside a function can be reference only in that function is know as local binding
- 5. Nested scope JavaScript distinguishes not just global and local binding only. Block and functions can be created inside other block and functions, producing multiple degree of locality. This set of binding is visible inside a block is determined by the place of that block in the program text. This approach to binding visibility is called lexical scoping.
- 6. Function as values We can use the function value as the other value. A function values can do all the thing that other values can do. It is possible to store a function values in a new binding, pass it as an argument to a function and so on. Similarly, a binding that holds a function is still just a regular binding and can it not constant, be assigned a new value like
- 7. cont.
- 8. Declaration notation There is a slightly shorter way to create a function binding. When the function keyword is used at the start of a statement, it works differently. function square(x) { return X*X; } this is a function declaration. The statement defines the binding square and points it at the given function.
- 9. Arrow functions Instead of function keyword, it uses an arrow (=>) made up of equals and greater-than character.
- 10. Cont.. The arrow comes after the list of parameters and is followed by the function’s body. When there is only one parameters we can omit the parentheses around the parameters list.
- 11. The call stack Once the function call is done then it will return to the main program the main program should maintain the log from which the function is called. The place where the computer stores this context is the call of stack. Every time the function is called, the current context is stored on the top of this stack. When function is returns, it removes the top context from the stack and uses the context to continue execution .
- 12. Cont..
- 13. Optional arguments JavaScript is extremely broad-minded about the number of arguments you pass to a function. If you pass to many, the extra ones are ignored. If you pass to few, the missing parameters get assigned the value undefined
- 14. Closure The ability to treat functions as values, combined with the fact that local binding are re-created every time a function is called. This allowed both the instances of the binding can still be accessed. This features –being able to reference a specific instance of a local binding in an enclosing scope is called closure.
- 15. example
- 16. Recursion
- 17. Cont.. A function that calls itself it recursive is know as recursion The calling function and the called function is same in recursion