这次我们来看一下angular的Sandboxing Angular Expressions。关于内置方法的，核心有两块：Lexer和Parser。其中大家对$parse可能更了解一点。好了不多废话，先看Lexer的内部结构：

1.Lexer

//构造函数var Lexer = function(options) { this.options = options;};//原型 Lexer.prototype = { constructor: Lexer, lex: function(){}, is: function(){}, peek: function(){ }, isNumber: function(){ }, isWhitespace: function(){}, isIdent: function(){}, isExpOperator: function(){}, throwError: function(){ }, readNumber: function(){ }, readIdent: function(){ }, readString: function(){ }};

这里指出一点，因为是表达式。所以类似"123"这类的东西，在Lexer看来应该算是数字而非字符串。表达式中的字符串必须使用单引号或者双引号来标识。Lexer的核心逻辑在lex方法中：

lex: function(text) { this.text = text; this.index = 0; this.tokens = []; while (this.index < this.text.length) { var ch = this.text.charAt(this.index); if (ch === '"' || ch === "'") { this.readString(ch); } else if (this.isNumber(ch) || ch === '.' && this.isNumber(this.peek())) { this.readNumber(); } else if (this.isIdent(ch)) { this.readIdent(); } else if (this.is(ch, '(){}[].,;:?')) { this.tokens.push({index: this.index, text: ch}); this.index++; } else if (this.isWhitespace(ch)) { this.index++; } else { var ch2 = ch + this.peek(); var ch3 = ch2 + this.peek(2); var op1 = OPERATORS[ch]; var op2 = OPERATORS[ch2]; var op3 = OPERATORS[ch3]; if (op1 || op2 || op3) { var token = op3 ? ch3 : (op2 ? ch2 : ch); this.tokens.push({index: this.index, text: token, operator: true}); this.index += token.length; } else { this.throwError('Unexpected next character ', this.index, this.index + 1); } } } return this.tokens; }

主要看一下匹配操作运算。这里源码中会调用OPERATORS。看一下OPERATORS：

var OPERATORS = extend(createMap(), { '+':function(self, locals, a, b) { a=a(self, locals); b=b(self, locals); if (isDefined(a)) { if (isDefined(b)) { return a + b; } return a; } return isDefined(b) ? b : undefined;}, '-':function(self, locals, a, b) { a=a(self, locals); b=b(self, locals); return (isDefined(a) ? a : 0) - (isDefined(b) ? b : 0); }, '*':function(self, locals, a, b) {return a(self, locals) * b(self, locals);}, '/':function(self, locals, a, b) {return a(self, locals) / b(self, locals);}, '%':function(self, locals, a, b) {return a(self, locals) % b(self, locals);}, '===':function(self, locals, a, b) {return a(self, locals) === b(self, locals);}, '!==':function(self, locals, a, b) {return a(self, locals) !== b(self, locals);}, '==':function(self, locals, a, b) {return a(self, locals) == b(self, locals);}, '!=':function(self, locals, a, b) {return a(self, locals) != b(self, locals);}, '<':function(self, locals, a, b) {return a(self, locals) < b(self, locals);}, '>':function(self, locals, a, b) {return a(self, locals) > b(self, locals);}, '<=':function(self, locals, a, b) {return a(self, locals) <= b(self, locals);}, '>=':function(self, locals, a, b) {return a(self, locals) >= b(self, locals);}, '&&':function(self, locals, a, b) {return a(self, locals) && b(self, locals);}, '||':function(self, locals, a, b) {return a(self, locals) || b(self, locals);}, '!':function(self, locals, a) {return !a(self, locals);}, //Tokenized as operators but parsed as assignment/filters '=':true, '|':true});

可以看到OPERATORS实际上存储的是操作符和操作符函数的键值对。根据操作符返回对应的操作符函数。我们看一下调用例子：

var _l = new Lexer({});var a = _l.lex("a = a + 1");console.log(a);

结合之前的lex方法，我们来回顾下代码执行过程：

1.index指向'a'是一个字母。匹配isIdent成功。将生成的token存入tokens中

2.index指向空格符，匹配isWhitespace成功，同上

3.index指向=，匹配操作运算符成功，同上

4.index指向空格符，匹配isWhitespace成功，同上

5.index指向'a'是一个字母。匹配isIdent成功。同上

7.index指向+，匹配操作运算符成功，同上

8.index指向空格符，匹配isWhitespace成功，同上

9.index指向1，匹配数字成功，同上

以上则是"a = a + 1"的代码执行过程。9步执行结束之后，跳出while循环。刚才我们看到了，每次匹配成功，源码会生成一个token。因为匹配类型的不同，生成出来的token的键值对略有不同：

number:{ index: start, text: number, constant: true, value: Number(number) },string: { index: start, text: rawString, constant: true, value: string },ident: { index: start, text: this.text.slice(start, this.index), identifier: true },'(){}[].,;:?': { index: this.index, text: ch},"操作符": { index: this.index, text: token, operator: true}//text是表达式，而value才是实际的值

number和string其实都有相对应的真实值，意味着如果我们表达式是2e2，那number生成的token的值value就应该是200。到此我们通过lexer类获得了一个具有token值得数组。从外部看，实际上Lexer是将我们输入的表达式解析成了token json。可以理解为生成了表达式的语法树（AST）。但是目前来看，我们依旧还没有能获得我们定义表达式的结果。那就需要用到parser了。

2.Parser

先看一下Parser的内部结构：

//构造函数var Parser = function(lexer, $filter, options) { this.lexer = lexer; this.$filter = $filter; this.options = options;};//原型Parser.prototype = { constructor: Parser, parse： function(){}, primary: function(){}, throwError: function(){ }, peekToken: function(){}, peek: function(){}, peekAhead: function(){ }, expect: function(){ }, consume: function(){ }, unaryFn: function(){ }, binaryFn: function(){ }, identifier: function(){}, constant: function(){}, statements: function(){}, filterChain: function(){}, filter: function(){}, expression: function(){}, assignment: function(){}, ternary: function(){}, logicalOR: function(){ }, logicalAND: function(){ }, equality: function(){ }, relational: function(){ }, additive: function(){ }, multiplicative: function(){ }, unary: function(){ }, fieldAccess: function(){}, objectIndex: function(){}, functionCall: function(){}, arrayDeclaration: function(){}, object: function(){}}

Parser的入口方法是parse，内部执行了statements方法。来看下statements：

statements: function() { var statements = []; while (true) { if (this.tokens.length > 0 && !this.peek('}', ')', ';', ']')) statements.push(this.filterChain()); if (!this.expect(';')) { // optimize for the common case where there is only one statement. // TODO(size): maybe we should not support multiple statements? return (statements.length === 1) ? statements[0] : function $parseStatements(self, locals) { var value; for (var i = 0, ii = statements.length; i < ii; i++) { value = statements[i](self, locals); } return value; }; } } }

这里我们将tokens理解为表达式，实际上它就是经过表达式通过lexer转换过来的。statements中。如果表达式不以},),;,]开头，将会执行filterChain方法。当tokens检索完成之后，最后返回了一个$parseStatements方法。其实Parser中很多方法都返回了类似的对象，意味着返回的内容将需要执行后才能得到结果。

看一下filterChain：

filterChain: function() { var left = this.expression(); var token; while ((token = this.expect('|'))) { left = this.filter(left); } return left; }

其中filterChain是针对angular表达式独有的"|"filter写法设计的。我们先绕过这块，进入expression

expression: function() { return this.assignment(); }

再看assignment：

assignment: function() { var left = this.ternary(); var right; var token; if ((token = this.expect('='))) { if (!left.assign) { this.throwError('implies assignment but [' + this.text.substring(0, token.index) + '] can not be assigned to', token); } right = this.ternary(); return extend(function $parseAssignment(scope, locals) { return left.assign(scope, right(scope, locals), locals); }, { inputs: [left, right] }); } return left; }

我们看到了ternary方法。这是一个解析三目操作的方法。与此同时，assignment将表达式以=划分成left和right两块。并且两块都尝试执行ternary。

ternary: function() { var left = this.logicalOR(); var middle; var token; if ((token = this.expect('?'))) { middle = this.assignment(); if (this.consume(':')) { var right = this.assignment(); return extend(function $parseTernary(self, locals) { return left(self, locals) ? middle(self, locals) : right(self, locals); }, { constant: left.constant && middle.constant && right.constant }); } } return left; }

在解析三目运算之前，又根据?将表达式划分成left和right两块。左侧再去尝试执行logicalOR，实际上这是一个逻辑与的解析，按照这个执行流程，我们一下有了思路。这有点类似我们一般写三目时。代码的执行情况，比如： 2 > 2 ? 1 : 0。如果把这个当成表达式，那根据?划分left和right，left就应该是2 > 2，right应该就是 1: 0。然后尝试在left看是否有逻辑或的操作。也就是，Parser里面的方法调用的嵌套级数越深，其方法的优先级则越高。好，那我们一口气看看这个最高的优先级在哪？

logicalOR -> logicalAND -> equality -> relational -> additive -> multiplicative -> unary

好吧，嵌套级数确实有点多。那么我们看下unary。

unary: function() { var token; if (this.expect('+')) { return this.primary(); } else if ((token = this.expect('-'))) { return this.binaryFn(Parser.ZERO, token.text, this.unary()); } else if ((token = this.expect('!'))) { return this.unaryFn(token.text, this.unary()); } else { return this.primary(); } }

这边需要看两个主要的方法，一个是binaryFn和primay。如果判断是-，则必须通过binaryFn去添加函数。看下binaryFn

binaryFn: function(left, op, right, isBranching) { var fn = OPERATORS[op]; return extend(function $parseBinaryFn(self, locals) { return fn(self, locals, left, right); }, { constant: left.constant && right.constant, inputs: !isBranching && [left, right] }); }

其中OPERATORS是之前聊Lexer也用到过，它根据操作符存储相应的操作函数。看一下fn(self, locals, left, right)。而我们随便取OPERATORS中的一个例子：

'-':function(self, locals, a, b) { a=a(self, locals); b=b(self, locals); return (isDefined(a) ? a : 0) - (isDefined(b) ? b : 0); }

其中a和b就是left和right，他们其实都是返回的跟之前类似的$parseStatements方法。默认存储着token中的value。经过事先解析好的四则运算来生成最终答案。其实这就是Parser的基本功能。至于嵌套，我们可以把它理解为js的操作符的优先级。这样就一目了然了。至于primay方法。塔刷选{ ( 对象做进一步的解析过程。

Parser的代码并不复杂，只是函数方法间调用密切，让我们再看一个例子：

var _l = new Lexer({});var _p = new Parser(_l);var a = _p.parse("1 + 1 + 2");console.log(a()); //4

我们看下1+1+2生成的token是什么样的：

[{"index":0,"text":"1","constant":true,"value":1},{"index":2,"text":"+","operator":true},{"index":4,"text":"1","constant":true,"value":1},{"index":6,"text":"+","operator":true},{"index":8,"text":"2","constant":true,"value":2}]

Parser根据lexer生成的tokens尝试解析。tokens每一个成员都会生成一个函数，其先后执行逻辑按照用户输入的1+1+2的顺序执行。注意像1和2这类constants为true的token，parser会通过constant生成需要的函数$parseConstant，也就是说1+1+2中的两个1和一个2都是返回$parseConstant函数，通过$parseBinaryFn管理加法逻辑。

constant: function() { var value = this.consume().value; return extend(function $parseConstant() { return value; //这个函数执行之后，就是将value值返回。 }, { constant: true, literal: true }); },binaryFn: function(left, op, right, isBranching) { var fn = OPERATORS[op];//加法逻辑 return extend(function $parseBinaryFn(self, locals) { return fn(self, locals, left, right);//left和right分别表示生成的对应函数 }, { constant: left.constant && right.constant, inputs: !isBranching && [left, right] }); }

那我们demo中的a应该返回什么函数呢？当然是$parseBinaryFn。其中的left和right分别是1+1的$parseBinaryFn，right就是2的$parseConstant。

再来一个例子：

var _l = new Lexer({});var _p = new Parser(_l);var a = _p.parse('{"name": "hello"}');console.log(a);

这边我们传入一个json，理论上我们执行完a函数，应该返回一个{name: "hello"}的对象。它调用了Parser中的object

object: function() { var keys = [], valueFns = []; if (this.peekToken().text !== '}') { do { if (this.peek('}')) { // Support trailing commas per ES5.1. break; } var token = this.consume(); if (token.constant) { //把key取出来 keys.push(token.value); } else if (token.identifier) { keys.push(token.text); } else { this.throwError("invalid key", token); } this.consume(':'); //冒号之后，则是值，将值存在valueFns中 valueFns.push(this.expression()); //根据逗号去迭代下一个 } while (this.expect(',')); } this.consume('}'); return extend(function $parseObjectLiteral(self, locals) { var object = {}; for (var i = 0, ii = valueFns.length; i < ii; i++) { object[keys[i]] = valueFns[i](self, locals); } return object; }, { literal: true, constant: valueFns.every(isConstant), inputs: valueFns }); }

比方我们的例子{"name": "hello"}，object会将name存在keys中，hello则会生成$parseConstant函数存在valueFns中，最终返回$parseObjectLiternal函数。

下一个例子：

var a = _p.parse('{"name": "hello"}["name"]');

这个跟上一个例子的差别在于后面尝试去读取name的值，这边则调用parser中的objectIndex方法。

objectIndex: function(obj) { var expression = this.text; var indexFn = this.expression(); this.consume(']'); return extend(function $parseObjectIndex(self, locals) { var o = obj(self, locals), //parseObjectLiteral，实际就是obj i = indexFn(self, locals), //$parseConstant，这里就是name v; ensureSafeMemberName(i, expression); if (!o) return undefined; v = ensureSafeObject(o[i], expression); return v; }, { assign: function(self, value, locals) { var key = ensureSafeMemberName(indexFn(self, locals), expression); // prevent overwriting of Function.constructor which would break ensureSafeObject check var o = ensureSafeObject(obj(self, locals), expression); if (!o) obj.assign(self, o = {}, locals); return o[key] = value; } }); }

很简单吧，obj[xx]和obj.x类似。大家自行阅读，我们再看一个函数调用的demo

var _l = new Lexer({});var _p = new Parser(_l, '', {});var demo = { "test": function(){ alert("welcome"); }};var a = _p.parse('test()');console.log(a(demo));

我们传入一个test的调用。这边调用了parser中的functionCall方法和identifier方法

identifier: function() { var id = this.consume().text; //Continue reading each `.identifier` unless it is a method invocation while (this.peek('.') && this.peekAhead(1).identifier && !this.peekAhead(2, '(')) { id += this.consume().text + this.consume().text; } return getterFn(id, this.options, this.text); }

看一下getterFn方法

...forEach(pathKeys, function(key, index) { ensureSafeMemberName(key, fullExp); var lookupJs = (index // we simply dereference 's' on any .dot notation ? 's' // but if we are first then we check locals first, and if so read it first : '((l&&l.hasOwnProperty("' + key + '"))?l:s)') + '.' + key; if (expensiveChecks || isPossiblyDangerousMemberName(key)) { lookupJs = 'eso(' + lookupJs + ', fe)'; needsEnsureSafeObject = true; } code += 'if(s == null) return undefined;\n' + 's=' + lookupJs + ';\n'; }); code += 'return s;'; var evaledFnGetter = new Function('s', 'l', 'eso', 'fe', code); // s=scope, l=locals, eso=ensureSafeObject evaledFnGetter.toString = valueFn(code);...

这是通过字符串创建一个匿名函数的方法。我们看下demo的test生成了一个什么匿名函数：

function('s', 'l', 'eso', 'fe'){if(s == null) return undefined;s=((l&&l.hasOwnProperty("test"))?l:s).test;return s;}

这个匿名函数的意思，需要传入一个上下文，匿名函数通过查找上下文中是否有test属性，如果没有传上下文则直接返回未定义。这也就是为什么我们在生成好的a函数在执行它时需要传入demo对象的原因。最后补一个functionCall

functionCall: function(fnGetter, contextGetter) { var argsFn = []; if (this.peekToken().text !== ')') { do { //形参存入argsFn argsFn.push(this.expression()); } while (this.expect(',')); } this.consume(')'); var expressionText = this.text; // we can safely reuse the array across invocations var args = argsFn.length ? [] : null; return function $parseFunctionCall(scope, locals) { var context = contextGetter ? contextGetter(scope, locals) : isDefined(contextGetter) ? undefined : scope; //或者之前创建生成的匿名函数 var fn = fnGetter(scope, locals, context) || noop; if (args) { var i = argsFn.length; while (i--) { args[i] = ensureSafeObject(argsFn[i](scope, locals), expressionText); } } ensureSafeObject(context, expressionText); ensureSafeFunction(fn, expressionText); // IE doesn't have apply for some native functions //执行匿名函数的时候需要传入上下文 var v = fn.apply ? fn.apply(context, args) : fn(args[0], args[1], args[2], args[3], args[4]); if (args) { // Free-up the memory (arguments of the last function call). args.length = 0; } return ensureSafeObject(v, expressionText); }; }

下面我们看一下$ParseProvider，这是一个基于Lex和Parser函数的angular内置provider。它对scope的api提供了基础支持。

...return function $parse(exp, interceptorFn, expensiveChecks) { var parsedExpression, oneTime, cacheKey; switch (typeof exp) { case 'string': cacheKey = exp = exp.trim(); var cache = (expensiveChecks ? cacheExpensive : cacheDefault); parsedExpression = cache[cacheKey]; if (!parsedExpression) { if (exp.charAt(0) === ':' && exp.charAt(1) === ':') { oneTime = true; exp = exp.substring(2); } var parseOptions = expensiveChecks ? $parseOptionsExpensive : $parseOptions; //调用lexer和parser var lexer = new Lexer(parseOptions); var parser = new Parser(lexer, $filter, parseOptions); parsedExpression = parser.parse(exp); //添加$$watchDelegate,为scope部分提供支持 if (parsedExpression.constant) { parsedExpression.$$watchDelegate = constantWatchDelegate; } else if (oneTime) { //oneTime is not part of the exp passed to the Parser so we may have to //wrap the parsedExpression before adding a $$watchDelegate parsedExpression = wrapSharedExpression(parsedExpression); parsedExpression.$$watchDelegate = parsedExpression.literal ? oneTimeLiteralWatchDelegate : oneTimeWatchDelegate; } else if (parsedExpression.inputs) { parsedExpression.$$watchDelegate = inputsWatchDelegate; } //做相关缓存 cache[cacheKey] = parsedExpression; } return addInterceptor(parsedExpression, interceptorFn); case 'function': return addInterceptor(exp, interceptorFn); default: return addInterceptor(noop, interceptorFn); } };

总结：Lexer和Parser的实现确实让我大开眼界。通过这两个函数，实现了angular自己的语法解析器。逻辑部分还是相对复杂

以上所述是小编给大家介绍的Angularjs 1.3 中的$parse实例代码，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对网站的支持！