JavaScript map(), reduce(), filter(), forEach(), call(), apply() and bind() polyfills

map_reduce_filter_forEach_call_apply_bind_polyfills.js

Call(), apply() and Bind() Implementation:

// Bind implementation
Function.prototype.myBind = function(...args) {
  let obj = this;
  let params = args.slice(1);
  return function(...args2) {
    
    return obj.apply(args[0], [...params, ...args2]);
  }
}


// call implementation
Function.prototype.myCall = function(context, ...args) {
    context.fnName = this;
    context.fnName(...args);
}

// apply implementation
Function.prototype.myApply = function(context, args) {
    context.fnName = this;
    context.fnName(...args);
}



map(), filter(), reduce() and forEach() Implementation:

// map() Implementation:
Array.prototype.myMap = function(callback) {
  const result = [];
  
  for(let i = 0; i < this.length; i++) {
    result.push(callback(this[i], i, this))
  }
  
  return result;
};


//filter() Implementation
Array.prototype.myFilter = function(callback) {
  const result = [];
  
  for(let i = 0; i < this.length; i++) {
    const eleResult = callback(this[i], i, this);
    if(eleResult) {
    result.push(this[i])
    }
  }
  
  return result;
};


// reduce() Implementation:
Array.prototype.myReduce = function(callback, initialValue) {
  let start = 0;
  var accumulator;
  if (initialValue) {
    accumulator = initialValue;
  } else {
    accumulator = this[0];
    start = 1;
  }
  
  for(let i = start; i < this.length; i++) {
    if(accumulator !== undefined) {
      accumulator = callback(accumulator, this[i], i, this);
    } else {
      accumulator = this[i]
    }
  }
  
  return accumulator;
};


// forEach Implementation:
Array.prototype.myForEach = function(callback) {
  for(let i = 0; i < this.length; i++) {
    callback(this[i], i, this);
    }
};