数组添加项

var fruits = ["apple", "banana", "cherries", "durian"];

fruits.push("grapes");
/*  [-,-,-,-,grapes]  */

fruits.unshift("grapes");
/*  [grapes,-,-,-,-]  */

fruits.splice(2, 0, "grapes");
/*  [-,-,grapes,-,-]  */

// Add after cherries
fruits.splice(fruits.indexOf("cherries") + 1, 0, "donkey");
/*  [-,-,-,"donkey",-]  */

// Add before cherries
fruits.splice(fruits.indexOf("cherries"), 0, "donkey");
/*  [-,-,"donkey",-,-]  */