revision:
The unshift() method adds the specified elements to the beginning of an array and returns the new length of the array.
unshift()
unshift(element0)
unshift(element0, element1)
unshift(element0, element1, /* … ,*/ elementN)
Parameters:
elementN : the elements to add to the front of the "arr".
const array1 = [1, 2, 3];
console.log(array1.unshift(4, 5));
// Expected output: 5
console.log(array1);
// Expected output: Array [4, 5, 1, 2, 3]
<div>
<p id="unshift-1"> </p>
<p id="unshift-2"> </p>
<p id="unshift-3"> </p>
<p id="unshift-4"> </p>
<p id="unshift-5"> </p>
<p id="unshift-6"> </p>
</div>
<script>
const arr = [1, 2];
document.getElementById("unshift-1").innerHTML = "original array : " + arr;
arr.unshift(0); // result of the call is 3, which is the new array length
// arr is [0, 1, 2]
document.getElementById("unshift-2").innerHTML = "unshift 0 : " + arr;
arr.unshift(-2, -1); // the new array length is 5
// arr is [-2, -1, 0, 1, 2]
document.getElementById("unshift-3").innerHTML = "unshift -2 -1 : " + arr;
arr.unshift([-4, -3]); // the new array length is 6
// arr is [[-4, -3], -2, -1, 0, 1, 2]
document.getElementById("unshift-4").innerHTML = "unshift -4 -3 : " + arr;
arr.unshift([-7, -6], [-5]); // the new array length is 8
// arr is [ [-7, -6], [-5], [-4, -3], -2, -1, 0, 1, 2 ]
document.getElementById("unshift-5").innerHTML = "unshift [-7 -6], [-5] : " + arr;
document.getElementById("unshift-6").innerHTML = "unshift : " + arr.length;
</script>
<div>
<p id="unshift-7"></p>
<p id="unshift-8"></p>
<p id="unshift-9"></p>
</div>
<script>
const fruits = [" Banana", " Orange", " Apple", " Mango"];
document.getElementById("unshift-7").innerHTML = "array : " + fruits
fruits.unshift(" Lemon", " Pineapple");
document.getElementById("unshift-8").innerHTML = "new array : " + fruits;
document.getElementById("unshift-9").innerHTML = "array length: " + fruits.unshift();
</script>