# Rest parameter `...`
By adding a rest parameter to a function, we can send an `n(0-Infinity)` number of arguments as an array. The rest parameter is prefixed (by `...`) and should always be the last argument of a function.

function testFn(...params) {
  for(let i = 0,l = params.length; i < l; i++){
    console.log(params[i]);
  }
}
testFn(1,2,3,4,5);

---
Let's create another function to calculate the sum  of numbers.

function sum(...params) {
    console.log(params);
    let sum = params.reduce((acc,val)=>{
        return acc + val;
    },0);
    return sum;

}
console.log("Calling sum(1,2)", sum(1,2));
console.log("Calling sum(1,2,3)", sum(1,2,3));
console.log("Calling sum(1,2,3,4)", sum(1,2,3,4));
console.log("Calling sum()", sum());

A single function can only have one rest parameter.

```
test(...prams1, ...params2, ...param3)
```
---
The rest parameter should be the last parameter of a function.

```
// wrong
test(prams1,...params2,param3);

test(prams1,params2,...param3);
```
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## Correct example 

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## Rest parameter is an Array
The type of the rest parameter is `Array`.

```js
function test(...restParam) {
    console.log(Array.isArray(restParam));
}
test();
```
---
## Difference between function `arguments` object and rest parameter

* The `arguments` object is not a real array, while rest parameters are `Array`.
* The rest parameter only contains the extra parameters; whereas, arguments contain all the parameters passed to the function (this includes the rest parameter as an array). 

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What is the rest parameter in JavaScript?

Rest parameters in JavaScript allow functions to handle an indefinite number of arguments as arrays and must be the last parameter.

What is the rest parameter in JavaScript?

Rest parameter ...

Correct example

Rest parameter is an Array

Difference between function arguments object and rest parameter

Rest parameter `...`

Difference between function `arguments` object and rest parameter