Polyfill Array.prototype.reduce

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**Approach:** Find first present index if no initialValue, then iterate, skipping holes. ```javascript Array.prototype.myReduce = function(callback, initialValue) { if (this == null) throw new TypeError('myReduce called on null'); if (typeof callback !== 'function') throw new TypeError('callback not a function'); const O = Object(this); const len = O.length >>> 0; let k = 0, acc; if (arguments.length > 1) acc = initialValue; else { while (k < len && !(k in O)) k++; if (k >= len) throw new TypeError('Reduce of empty array with no initial value'); acc = O[k++]; } for (; k < len; k++) if (k in O) acc = callback(acc, O[k], k, O); return acc; }; // Demo console.log([1,2,3].myReduce((a,b)=>a+b, 0)); // 6 console.log([1,2,3].myReduce((a,b)=>a+b)); // 6 (no init) console.log([,1,,2].myReduce((a,b)=>a+b, 0)); // 3 (skips holes) try { [].myReduce((a,b)=>a+b); } catch(e) { console.log(e.message.includes('empty')); } // true console.log(['a','b','c'].myReduce((a,b)=

Polyfill Array.prototype.reduce

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