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Additional methods for Array
Here are a bunch of additional methods for Array which I find quite useful. They work with values rather than position.
Download plain js Download minified or have a look at the source at the bottom of this page.
When you have these new tools in your toolbox you can often perform complex tasks with great simplicity. All you need to do is think about sets of data rather than each element. That is, you have an array and you want it to have certain characteristics. For example:
Beforeput item in list of used items
Nowused item list tells us which items have been used
What's the difference? Well, if we use an item more than once do we want to to appear in the list more than once? From the description above I'd say no. So instead of usedList.push(item); you'd use usedList.append(item);

.append(Value) Same as .push() but only if the value is not in subject already
Returns true if added else false
.concatExtra(AnArray) Add elements of AnArray to end of subject, but only if they don't appear already in the subject. Return changed subject. (If AnArray isn't an array then whatever it is will be .append()-ed).
.deduplicate() Deduplicate in-situ
.insert(Value, After|MatchFun, Before Flag) Place a new value at a particular place based on either an existing value or a function. Return true if the searched-for value was found or the function returned true.
If the BeforeFlag is truthy then instead of inserting after the matched value, place it in before.
The match function is what you'd give to .findIndex(). Examples:
var a = [1,2,3,4,5]; a.insert('threeA',3); // [1,2,3,"threeA",4,5] a.insert(3.1,(EL=>typeof El == 'string'),true); // [1,2,3,3.1,"threeA",4,5]
.intersection(AnArray) Return an array of elements appearing in both. The order follows the order of the subject array
var a123 = [1,2,3]; var a432 = [4,3,2]; These give slightly different results var twoThree = a123.intersection(a432); var threeTwo = a432.intersection(a123);
.missingFrom(AnArray) Return an array of elements appearing this array but not the AnArray.
The order follows the order of the subject array
.remove(Value|FilterFunction) Return changed subject.
This only removes a single Value but if a filter function is provided then all matches will be removed. (Then it's equivalent to myArray=myArray.filter(A negitivised version of the filter) )
.sortOnData(IxOrName) Sort in-situ according to a given index or object property/method name.
If elements are arrays then provide a numeric index.
If elements are objects then give name of field.
.substitute(OldValue,NewValue) Return true if OldValue found, otherwise false
.unconcat(AnArray) Weed an array of values from the subject. Return changed subject.
Note: If AnArray isn't an array then it will be .remove()-ed

// In-situ array modification by value // Extending Array.prototype //==================================== // append(Value) // Same as .push() but only if not in subject already // Returns true if added else false //---------------------------------------------------- Object.defineProperty(Array.prototype, 'append', { enumerable: false, value: function(Value){ if(this.includes(Value)===false){ this.push(Value); return true; }else{ return false; } } }); // concatExtra(AnArray) // Add elements of AnArray to end of subject, but only // if they don't appear already in the subject // Return changed subject // Note: If AnArray isn't an array then whatever it is // will be .append()-ed //---------------------------------------------------- Object.defineProperty(Array.prototype, 'concatExtra', { enumerable: false, value: function(AnArray){ var a = Array.isArray(AnArray) ? AnArray : [AnArray]; a.forEach(function(A){ this.append(A); },this); return this; } }); // remove(Value|FilterFunction) // Return changed subject //---------------------------------------------------- Object.defineProperty(Array.prototype, 'remove', { enumerable: false, value: function(ValueOrFilter){ var ix; if(typeof ValueOrFilter == 'function'){ ix = this.length - 1; while(ix>=0){ if(ValueOrFilter(this[ix])){ this.splice(ix,1); } ix--; } }else{ ix = this.indexOf(ValueOrFilter); if(ix > -1){ this.splice(ix,1); } } return this; } }); // unconcat(AnArray) // weed array of values from the subject that appear in the argument // Return changed subject. // Note: If AnArray isn't an array then it will be .remove()-ed //---------------------------------------------------- Object.defineProperty(Array.prototype, 'unconcat', { enumerable: false, value: function(AnArray){ var a = Array.isArray(AnArray) ? AnArray : [AnArray]; a.forEach(function(A){ this.remove(A); },this); return this; } }); // substitute(OldValue,NewValue) // Return boolean for success //---------------------------------------------------- Object.defineProperty(Array.prototype, 'substitute', { enumerable: false, value: function(OldValue,NewValue){ var ix = this.indexOf(OldValue); if(ix > -1){ this.splice(ix,1,NewValue); return true; }else{ return false; } } }); // insert(Value,After|MatchFun,Before Flag) // Return boolean for success //---------------------------------------------------- Object.defineProperty(Array.prototype, 'insert', { enumerable: false, value: function(Value,AfterOrMatch,Before){ var ix; if(typeof AfterOrMatch == 'function'){ ix = this.findIndex(AfterOrMatch); }else{ ix = this.indexOf(AfterOrMatch); } if(ix > -1){ if(Before){ix--;} this.splice(ix+1,0,Value); return true; }else{ return false; } } }); // intersection(AnArray) // Return an array of elements appearing in both. // The order follows the order of the subject array //---------------------------------------------------- Object.defineProperty(Array.prototype, 'intersection', { enumerable: false, value: function(AnArray){ var rv = []; this.forEach(function(V){ if(AnArray.includes(V)){ rv.push(V); } }); return rv; } }); // missingFrom(AnArray) // Return an array of elements appearing this array // but not the argument // The order follows the order of the subject array //---------------------------------------------------- Object.defineProperty(Array.prototype, 'missingFrom', { enumerable: false, value: function(AnArray){ var rv = []; this.forEach(function(V){ if(!AnArray.includes(V)){ rv.push(V); } }); return rv; } }); // deduplicate in-situ //---------------------------------------------------- Object.defineProperty(Array.prototype, 'deduplicate', { enumerable: false, value: function(){ var i = 0; while(i < this.length){ var el = this[i]; while(true){ var f = this.indexOf(el,i+1); if(f == -1){break;} this.splice(f,1); } i++; } return this; } }); // sort in-situ according to a given index or name // If elements are arrays then provide a numeric index // If elements are objects then give name of field //----------------------------------------------------- Object.defineProperty(Array.prototype, 'sortOnData', { enumerable: false, value: function(IxOrName){ this.sort(function(A,B){ if(A[IxOrName]<B[IxOrName]){ return -1; }else{ if(A[IxOrName]>B[IxOrName]){ return 1; }else{ return 0; } } }); } });