ST overflow

by Lamik

HTML

This snippet only presents tested code (it not perform tests)

JavaScript

//  https://stackoverflow.com/a/61406956/860099
  
    function AI(arr, i, el) {
      arr.splice(i, 0, el);
      return arr;
    }

    function BI(arr, i, el) {
      Array.prototype.splice.apply(arr, [i, 0, el]);
      return arr;
    }

    function CI(arr, i, el) {
      Array.prototype.splice.call(arr, i, 0, el);
      return arr;
    }

    function D(arr, i, el) {
      return arr.slice(0, i).concat(el, arr.slice(i));
    }

    function E(arr, i, el) {
      return [...arr.slice(0, i), el, ...arr.slice(i)]
    }

    function F(arr, i, el) {
      return arr.reduce((s, a, j)=> (j-i ? s.push(a) : s.push(el, a), s), []);
    }



    // -------------
    // TEST
    // -------------

    let arr = ["a", "b", "c", "d", "e", "f"];

    let log = (n, f) => {
      let a = f([...arr], 3, "NEW");
      console.log(`${n}: [${a}]`);
    };

    log('AI', AI);
    log('BI', BI);
    log('CI', CI);
    log('D', D);
    log('E', E);
    log('F', F);