调试中...
arr =
[1,2,3]
callback =
function(val, i, arr){ arr[i] = val * 2 }
context =
{"context": true}
[1,2,3]
function(val, i, arr){ arr[i] = val * 2 }
{"context": true}
[true, true, false, false]
function(val, i, arr){ arr[i] = this }
{"context": false}
[true, true, false, false]
function(val, i, arr){ arr[i] = !val }
{"context": 5}