var array1 = [ "要素2", "要素3", "要素4", "要素5" ];
var array2 = [ 2, 3, 4, 5 ];

array1 = []; //配列を空にします
array2 = []; //配列を空にします

var array3 = [ "b", "c", "d", "e"];
var array4 = [ "い", "う", "え", "お"];

array3.length = 0; //配列を空にします
array4.length = 0; //配列を空にします

console.log(array1);
console.log(array2);
console.log(array3);
console.log(array4);

//console.log()の結果
//array1 → []
//array2 → []
//array3 → []
//array4 → []