Array methods tips and tricks

1. shift and unshiftarr.shift() – extracts an item from the beginning,
   arr.unshift(...items) – adds items to the beginning.
   
2. splice: 
   The arr.splice(str) method is a swiss army knife for arrays. It can do everything: insert, remove and replace elements.
   arr.splice(index[, deleteCount, elem1, ..., elemN])
   
3. thisArg:
   Almost all array methods that call functions – like find, filter, map, with a notable exception of sort, accept an optional additional parameter thisArg.
   arr.find(func, thisArg);
   arr.filter(func, thisArg);
   arr.map(func, thisArg);
   // ...
   // thisArg is the optional last argument
   The value of thisArg parameter becomes this for func.
   
4. concat:arr.concat(arg1, arg2...)
   argN: not always an array
   If an argument argN is an array, then all its elements are copied. Otherwise, the argument itself is copied.
   Eg:
   let arr = [1, 2];
   alert( arr.concat([3, 4])); // 1,2,3,4
   alert( arr.concat([3, 4], [5, 6])); // 1,2,3,4,5,6
   alert( arr.concat([3, 4], 5, 6)); // 1,2,3,4,5,6 //one arg is an array, rest two are numbers


5. Sort numeric arraylet arr = [ 1, 2, 15 ];
   // the method reorders the content of arr
   arr.sort();
   alert( arr );  // 1, 15, 2
   Solution: Pass a comparison function as the first argument to sort function.
   Eg: arr.sort(function(a, b) { return a - b; });

src: http://javascript.info/array-methods