console 命令行工具 X clear

> ["redwood","bay","cedar",null,"maple"]
> 5
> undefined
> undefined
> false

console

var trees = new Array("redwood", "bay", "cedar", "oak", "maple");
delete trees[3];
// trees[3] =undefined
console.log(trees)
console.log(trees.length)
console.log(trees[3])
console.log(typeof trees[3])
console.log(3 in trees)