這次我們來(lái)看一下angular的Sandboxing Angular Expressions。關(guān)于內(nèi)置方法的，核心有兩塊：Lexer和Parser。其中大家對(duì)$parse可能更了解一點(diǎn)。好了不多廢話，先看Lexer的內(nèi)部結(jié)構(gòu)：

1.Lexer

//構(gòu)造函數(shù)var Lexer = function(options) { this.options = options;};//原型 Lexer.prototype = { constructor: Lexer, lex: function(){}, is: function(){}, peek: function(){ /* 返回表達(dá)式的下一個(gè)位置的數(shù)據(jù)，如果沒(méi)有則返回false */ }, isNumber: function(){ /* 判斷當(dāng)前表達(dá)式是否是一個(gè)數(shù)字 */ }, isWhitespace: function(){/* 判斷當(dāng)前表達(dá)式是否是空格符 */}, isIdent: function(){/* 判斷當(dāng)前表達(dá)式是否是英文字符(包含_和$) */}, isExpOperator: function(){/* 判斷當(dāng)時(shí)表達(dá)式是否是-，+還是數(shù)字 */}, throwError: function(){ /* 拋出異常 */}, readNumber: function(){ /* 讀取數(shù)字 */}, readIdent: function(){ /* 讀取字符 */}, readString: function(){ /*讀取攜帶''或""的字符串*/ }};

 這里指出一點(diǎn)，因?yàn)槭潜磉_(dá)式。所以類(lèi)似"123"這類(lèi)的東西，在Lexer看來(lái)應(yīng)該算是數(shù)字而非字符串。表達(dá)式中的字符串必須使用單引號(hào)或者雙引號(hào)來(lái)標(biāo)識(shí)。Lexer的核心邏輯在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 === "'") {  /* 嘗試判斷是否是字符串 */  this.readString(ch);  } else if (this.isNumber(ch) || ch === '.' && this.isNumber(this.peek())) {  /* 嘗試判斷是否是數(shù)字 */  this.readNumber();  } else if (this.isIdent(ch)) {  /* 嘗試判斷是否是字母 */  this.readIdent();  } else if (this.is(ch, '(){}[].,;:?')) {  /* 判斷是否是(){}[].,;:? */  this.tokens.push({index: this.index, text: ch});  this.index++;  } else if (this.isWhitespace(ch)) {  /* 判斷是否是空白符 */  this.index++;  } else {  /* 嘗試匹配操作運(yùn)算 */  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運(yùn)算。這里源碼中會(huì)調(diào)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});