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Skip function parameter in javascript

When we see “…” operator in the code, it is either rest parameters or the spread syntax.

There’s an one of easy way to distinguish between them:

⦁ When … operator is at the end of function parameters, it’s “rest parameters” and gathers the rest of the list of arguments into an array.
⦁ When … operator occurs in a function call or alike, it’s called a “spread syntax” and expands an array into a list.

Use patterns:

Rest parameters are used to create javascript functions that accept any number of arguments.
The spread(…) syntax is used to pass an array to javascript functions that normally require a list of many arguments.
Together they help to travel between a list and an array of parameters([…arr])with ease.

javascript skip default parameter:

function myfunc(x,y=2,z=6){
myfunc(5) //Output: 10 6
myfunc(5,4,2) //Output: 20 2
myfunc(5,undefined,17) //Output 10 17

skip arguments in js:

function userInfo(firstName, lastName, userName){
// other logic stuff
console.log(firstName, lastName, userName);
// skip lastName argument using: ...[,] and it's mean undefine
// 1 argument for ...[,] 2 arguments for ...[,,] and so on.....
userInfo('JavaScript', ...[,], 'js');
//it's mean => firstName: JavaScript, lastName: undefined, userName: js


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