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Functions are the bread and butter of JavaScript programming.

- ELOQUENT JAVASCRIPT

• The " Functions " is a concept of wrapping a piece of program in a value which has many uses.

• It helps us to structure the large chunk of a program in order to overcome repetition.

• It helps to associate names with subprograms and to isolate these subprograms from each other.

DEFINING A FUNCTION

A Function definition is a regular binding where the value of the binding is a Function.

Example:-

const square = function(x)
{
  return x * x;
};
console.log(square(12));
//144

The above code defines square which is the " function " that squares the given number. A function is created with an expression that starts with the keyword function.

1. Functions have a set of parameters and a body, which contains the statements that are to be executed when the function is called.

2. The function body of a function which is created this way must always be wrapped in braces, even when it consists of only a single statement.

3. A function can have multiple parameters or no parameters at all.

   Example:-

    -------------------------------------------------(no parameters)
    const makeNoise = function()
    {
    console.log("TingTing!");
    };
    makeNoise();
    // TingTing!
   
    --------------------------------------------------(multipe parameters)
    const power = function(base, exponent)
    {
    let result = 1;
    for (let count = 0; count < exponent; count++)
       {
          result *=base;
       }
    return result;
    };
    console.log(power(2, 10));
    // 1024
   

   In above example " makeNoise " does not list any parameter names.

4. Some functions produce a value such as power and square and some does not produce any value such as makeNoise.

5. A return statement determines the value the function which returns. when control comes across such a statement, it immediately jumps out of the current function and gives the returned value to the code which called the function.

6. A " return " keyword without an expression causes the function to return " undefined " .

7. Functions that don't have a " return " statement at all, such as " makeNoise ", returns undefined.

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.