[4, 5, 6, 7].at(1)         // 5
[4, 5, 6, 7].push(8)       // [4, 5, 6, 7, 8]
[4, 5, 6, 7].pop()         //[4, 5, 6, ]
[4, 5, 6, 7].fil(1)        //[1, 1, 1, 1]
[4, 5, 6, 7].join(' ')     //'4 5 6 7 '(string)
[4, 5, 6, 7].shift()       //[ 5, 6, 7]
[4, 5, 6, 7].reverse()     //[7, 6, 5, 4]
[4, 5, 6, 7].unshift(3)    // [3, 4, 5, 6, 7]
[4, 5, 6, 7].includes(6)   //true
[4, 5, 6, 7].map(item => 2*item) // [8, 10, 12, 14]
[4, 5, 6, 7].filter(item => item > 5)  //[6,7]
[4, 5, 6, 7].find(item => item > 5)    //6 (first match)
[4, 5, 6, 7].every(item => item > 0)   // true
[4, 5, 6, 7].findIndex(item => item === 5)  // 1
[4, 5, 6, 7].reduce((prev, curr) => prev+curr, 0)   //22