...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);
function multiple(multiplier, ... multiplicant) {console.log(Array.isArray(multiplicant));multiplicant.forEach(val=>{console.log(`${val} * ${multiplier} = ${val* multiplier}`);});}multiple(9, 1,2,3,4,5,6,7,8,9,10)
The type of the rest parameter is Array.
function test(...restParam) {
console.log(Array.isArray(restParam));
}
test();
arguments object and rest parameterarguments object is not a real array, while rest parameters are Array.