Array in javascript, is often used when we want to store list of elements and access them by a single variable. Here you are going to learn and understand easily the applications of arrays methods where and when needed.

To add/remove elements:

• push(...items) – adds items to the end,

• pop() – extracts an item from the end,

• shift() – extracts an item from the beginning,

• unshift(...items) – adds items to the beginning.

• concat(...items) – returns a new array: copies all members of the current one and adds items to it. If any of items is an array, then its elements are taken.

• slice(start, end) – creates a new array, copies elements from index start till end (not inclusive) into it.

• splice(pos, deleteCount, ...items) – at index pos deletes deleteCount elements and inserts items.

PRACTICE:

To search among elements:

• indexOf/lastIndexOf(item, pos) – look for item starting from position pos, return the index or -1 if not found.

• includes(value) – returns true if the array has value, otherwise false.

• find/filter(func) – filter elements through the function, return first/all values that make it return true. findIndex is like find, but returns the index instead of a value. To iterate over elements:

• forEach(func) – calls func for every element, does not return anything.

PRACTICE:

To transform the array:

• map(func) – creates a new array from results of calling func for every element.

• sort(func) – sorts the array in-place, then returns it.

• reverse() – reverses the array in-place, then returns it.

• split/join – convert a string to array and back.

• reduce/reduceRight(func, initial) – calculate a single value over the array by calling func for each element and passing an intermediate result between the calls.

Additionally:

• arr.some(fn)/arr.every(fn) check the array.

The function fn is called on each element of the array similar to map. If any/all results are true, returns true, otherwise false.

These methods behave sort of like || and && operators: if fn returns a truthy value, arr.some() immediately returns true and stops iterating over the rest of items; if fn returns a falsy value, arr.every() immediately returns false and stops iterating over the rest of items as well.

We can use every to compare arrays:

function arraysEqual(arr1, arr2) { return arr1.length === arr2.length && arr1.every((value, index) => value === arr2[index]); }

PRACTICE:

CONCLUSION

This has covered 80 percent of what you should know in array methods. Constant practice will make all the methods to stick in the brain.