uglifyjs与AST
Updated:
UglifyJS 提供了一些工具用于分析JavaScript代码，包括：
- parser，把 JavaScript 代码解析成抽象语法树
- code generator，通过抽象语法树生成代码
- compressor， 压缩 JavaScript代码
- mangler，混淆 JavaScript 代码
- scope analyzer，分析变量定义的工具
- tree walker，遍历树节点
- tree transformer，改变树节点
parser生成抽象语法树
UglifyJS.parse可将code解析成抽象语法树1
2var toplevel = UglifyJS.parse(code);
console.log(JSON.stringify(toplevel.body[0]));
将下面代码进行parse操作：1
2var key = "Hello";
console.log(key);
得到的结果为:1
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270[
{
"end":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":18,
"endcol":18,
"endline":1,
"pos":17,
"col":17,
"line":1,
"value":";",
"type":"punc"
},
"start":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":3,
"endcol":3,
"endline":1,
"pos":0,
"col":0,
"line":1,
"value":"var",
"type":"keyword"
},
"definitions":[
{
"end":{
"raw":""Hello"",
"file":null,
"comments_before":[],
"nlb":false,
"endpos":17,
"endcol":17,
"endline":1,
"pos":10,
"col":10,
"line":1,
"value":"Hello",
"type":"string",
"quote":"""
},
"start":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":7,
"endcol":7,
"endline":1,
"pos":4,
"col":4,
"line":1,
"value":"key",
"type":"name"
},
"value":{
"end":{
"raw":""Hello"",
"file":null,
"comments_before":[],
"nlb":false,
"endpos":17,
"endcol":17,
"endline":1,
"pos":10,
"col":10,
"line":1,
"value":"Hello",
"type":"string",
"quote":"""
},
"start":{
"raw":""Hello"",
"file":null,
"comments_before":[],
"nlb":false,
"endpos":17,
"endcol":17,
"endline":1,
"pos":10,
"col":10,
"line":1,
"value":"Hello",
"type":"string",
"quote":"""
},
"quote":""",
"value":"Hello"
},
"name":{
"end":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":7,
"endcol":7,
"endline":1,
"pos":4,
"col":4,
"line":1,
"value":"key",
"type":"name"
},
"start":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":7,
"endcol":7,
"endline":1,
"pos":4,
"col":4,
"line":1,
"value":"key",
"type":"name"
},
"name":"key"
}
}
]
},
{
"end":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":37,
"endcol":17,
"endline":2,
"pos":36,
"col":16,
"line":2,
"value":";",
"type":"punc"
},
"start":{
"file":null,
"comments_before":[],
"nlb":true,
"endpos":27,
"endcol":7,
"endline":2,
"pos":20,
"col":0,
"line":2,
"value":"console",
"type":"name"
},
"body":{
"end":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":36,
"endcol":16,
"endline":2,
"pos":35,
"col":15,
"line":2,
"value":")",
"type":"punc"
},
"start":{
"file":null,
"comments_before":[],
"nlb":true,
"endpos":27,
"endcol":7,
"endline":2,
"pos":20,
"col":0,
"line":2,
"value":"console",
"type":"name"
},
"args":[
{
"end":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":35,
"endcol":15,
"endline":2,
"pos":32,
"col":12,
"line":2,
"value":"key",
"type":"name"
},
"start":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":35,
"endcol":15,
"endline":2,
"pos":32,
"col":12,
"line":2,
"value":"key",
"type":"name"
},
"name":"key"
}
],
"expression":{
"end":{
"file":null,
"comments_before":[],
"nlb":false,
"endpos":31,
"endcol":11,
"endline":2,
"pos":28,
"col":8,
"line":2,
"value":"log",
"type":"name"
},
"start":{
"file":null,
"comments_before":[],
"nlb":true,
"endpos":27,
"endcol":7,
"endline":2,
"pos":20,
"col":0,
"line":2,
"value":"console",
"type":"name"
},
"property":"log",
"expression":{
"end":{
"file":null,
"comments_before":[],
"nlb":true,
"endpos":27,
"endcol":7,
"endline":2,
"pos":20,
"col":0,
"line":2,
"value":"console",
"type":"name"
},
"start":{
"file":null,
"comments_before":[],
"nlb":true,
"endpos":27,
"endcol":7,
"endline":2,
"pos":20,
"col":0,
"line":2,
"value":"console",
"type":"name"
},
"name":"console"
}
}
}
}
]
transformer的用法
1 | function before(node, descend) { ... }; |
“before” visitor
在树中的每一个节点， before visitor在遍历子节点之前被调用。它接受2个参数，现在的节点和子函数。
- before visitorf返回undefined:
如果后续访问者存在，遍历树会复制当前节点并进入处理子节点然后调用after visitor,
如果没有after visitor， 它将直接处理当前节点。 - 如果before visitor 返回了一个值，则当前节点会被这个值替换。它的子节点不会被处理，after visitor也不会被调用。
“after” visitor
如果你使用了after visitor, 它只有在before visitor返回undefined，节点被复制的时候才会被调用。如果after visitor返回的不是undefined，则现节点的值将被这个返回值覆盖。