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. If any/all results are true, returns true, otherwise false. The function fn is called on each element of the array similar to map. But there are few others:Īrr.some(fn)/ arr.every(fn) check the array. These methods are the most used ones, they cover 99% of use cases. Please note that methods sort, reverse and splice modify the array itself.
Array.isArray(value) checks value for being an array, if so returns true, otherwise false. 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. split/join – convert a string to array and back. 
reverse() – reverses the array in-place, then returns it. sort(func) – sorts the array in-place, then returns it. map(func) – creates a new array from results of calling func for every element. forEach(func) – calls func for every element, does not return anything. findIndex is like find, but returns the index instead of a value. find/filter(func) – filter elements through the function, return first/all values that make it return true. includes(value) – returns true if the array has value, otherwise false. indexOf/lastIndexOf(item, pos) – look for item starting from position pos, return the index or -1 if not found. 
If any of items is an array, then its elements are taken.
concat(.items) – returns a new array: copies all members of the current one and adds items to it. slice(start, end) – creates a new array, copies elements from index start till end (not inclusive) into it. 
items) – at index pos deletes deleteCount elements and inserts items.
unshift(.items) – adds items to the beginning. shift() – extracts an item from the beginning,. 
The latter is used more often, as it’s a bit easier to understand for most people. Return user.age >= this.minAge & user.age army.canJoin(user)), that does the same.
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