Nodejs Array First Predicate first(fn)

Method Source Code

// Returns first element in array, or first element that matches a predicate fn

Array.prototype.first = function(fn) {

    // Prototypes throw TypeErrors when the context or arguments are invalid

    if (Object.prototype.toString.call(this) !== '[object Array]') {
        throw new TypeError("`this` must be Array, not " + typeof this);
    }//from   w w  w .j a  v  a 2 s.c o  m

    // No predicate? Return first element

    if (typeof fn === 'undefined') {
        return this[0];
    }

    // Return first element that meets predicate

    if (typeof fn !== 'function') {
        throw new TypeError("Optional `argument[0]` must be predicate function if defined");
    }

    for (var i = 0, l = this.length; i < l; i++) {
        var element = this[i];
        if (fn.call(this, element, i, this)) {
            return element;
        }
    }
};

Related

1. first(f)

   Array.prototype.first = function(f){
       var i = 0;
       while(i < this.length){
           if(f == undefined){
               return this[i];
           if(f(this[i])){
              return this[i];
           i++;
       return null;
   };
   

2. first(func)

   Array.prototype.first = function(func) {
     return this.where(func)[0];
   };
   

3. first(func)

   Array.prototype.first = function(func) {
       var result = [];
       for(var i=0;i<this.length;i++) 
           if (func(this[i]))
               return this[i];
       return null;
   

4. first(func)

   Array.prototype.first = function (func) {
       var length = this.length,
           item = null;
       for (var i = 0; i < length; i++) {
           if (func(this[i])) {
               return this[i];
       return item;
   ...
   

5. first(matching)

   Array.prototype.first = function(matching) {
       for (var i = 0; i < this.length; i++) {
     var entry = this[i];
     if (matching(entry) == true)
         return this[i];
       return null;