The default, spread, and rest parameters were added in ES6.
Default Parameter: It is used to give the default values to the arguments, if no parameter is provided in the function call.
Syntax:
function fnName(param1 = defaultValue1, ..., paramN = defaultValueN) {
...
}
Example 1: In the below example, the first function gives result 7 whereas the second function call will be “undefined” as we did not pass any second argument.
Javascript
<script> function add(a, b) { return a + b } console.log(add(5, 2)); // 7 console.log(add(5)); // NaN </script> |
Output:
7 NaN
Example 2: In this example, we use default parameters in which we generally give a default value if no argument is provided. We take a default value of “b” so that in the second function call, we are not providing any argument, and its default value is taken.
Javascript
<script> function add(a, b = 3) { return a + b } console.log(add(5, 2)) console.log(add(5)) </script> |
Output:
7 8
Spread Operator: It is another operator provided through ES6 it generally spreads data of array/list.
In the following example, we are calculating min of all the numbers
Example 1:
Javascript
<script> console.log(Math.min(1, 2, 3, -1)); </script> |
Output:
-1
Example 2: Consider that we have an array instead of a list then the above min() function will not work and it will give “NaN”.
Javascript
<script> // Without spread operator let arr = [1, 2, 3, -1]; console.log(Math.min(arr)); // NaN </script> |
Output:
NaN
Example 3: When …arr is used, it generally spreads the arr values in the min() function.
Javascript
<script> // Spread operator let arr = [1, 2, 3, -1]; console.log(Math.min(...arr)); // -1 </script> |
Output:
-1
Rest Operator: It allows a function to accept an indefinite number of arguments if we are not sure how many arguments will receive.
Syntax:
function f(a, b, ...args) {
...
}
Example: In the below example, we are using the rest parameter which allows taking indefinite parameters.
Javascript
<script> function myFun(a, b, ...manyMoreArgs) { console.log("a", a) console.log("b", b) console.log("manyMoreArgs", manyMoreArgs) } myFun("one", "two", "three", "four", "five", "six"); </script> |
Output:
