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var a = [1, 2, 3];
var b = a.unshift(0);
console.log(a); //[0, 1, 2, 3]
console.log(b); //4(結果配列の要素数)
var a = [1, 2, 3];
var b = a.shift();
console.log(a); //[2, 3]
console.log(b); //1
var a = [1, 2, 3];
var b = a.pop();
console.log(a); //[1, 2]
console.log(b); //3
var a = [1, 2, 3];
var b = a.push(4);
console.log(a); //[1, 2, 3, 4]
console.log(b); //4(結果配列の要素数)