JavaScript implements its own DOM selector principle and code_javascript skills

Interpreter mode (Interpreter): Define a syntax format, execute it through program interpretation and complete corresponding tasks. In front-end programming scenarios, the interpreter mode can be applied to interpret CSS selectors to select DOM elements.

Open and closed principle: The open and closed principle in object-oriented is that a class or module should be open to extension and closed to modification. In this dom selector, the id selector and element selector are implemented. Class selector, if you need an attribute selector in the future, define an attribute selector to implement the corresponding method, and add the corresponding branch to create an attribute selector object in the simple factory.

Matching principle: Browsers match CSS selectors from right to left, so when implementing your own DOM selector, the matching behavior should be consistent with the native matching behavior of the browser. .

Code:

Copy code The code is as follows:

(function (ns) {
/*
//tagName
console.log(dom.get("p"));
//#id
console.log(dom.get("#div"));
//.class
console.log(dom.get(".span", document.body));
//tag.class
console.log(dom.get("div.span"));
//#id .class
console.log(dom.get("#div .span"));
//.class .class
console.log(dom.get(".ul .li-test"));
*/
var doc = document;
var simple = /^(?:#|.)?([w-_] )/;
function api(query, context) {
context = context || doc;
//调用原生选择器
if(!simple.test(query) && context.querySelectorAll){
return context.querySelectorAll(query);
}else {
//调用自定义选择器
return interpret(query, context);
}
}
//解释执行dom选择符
function interpret(query, context){
var parts = query.replace(/s /, " ").split(" ");
var part = parts.pop();
var selector = Factory.create(part);
var ret = selector.find(context);
return (parts[0] && ret[0]) ? filter(parts, ret) : ret;
}
//ID选择器
function IDSelector(id) {
this.id = id.substring(1);
}
IDSelector.prototype = {
find: function (context) {
return document.getElementById(this.id);
},
match: function(element){
return element.id == this.id;
}
};
IDSelector.test = function (selector) {
var regex = /^#([w-_] )/;
return regex.test(selector);
};
//元素选择器
function TagSelector(tagName) {
this.tagName = tagName.toUpperCase();
}
TagSelector.prototype = {
find: function (context) {
return context.getElementsByTagName(this.tagName);
},
match: function(element){
return this.tagName == element.tagName.toUpperCase() || this.tagName === "*";
}
};
TagSelector.test = function (selector) {
var regex = /^([w*-_] )/;
return regex.test(selector);
};
//类选择器
function ClassSelector(className) {
var splits = className.split('.');
this.tagName = splits[0] || undefined ;
this.className = splits[1];
}
ClassSelector.prototype = {
find: function (context) {
var elements;
var ret = [];
var tagName = this.tagName;
var className = this.className;
var selector = new TagSelector((tagName || "*"));
//支持原生getElementsByClassName
if (context.getElementsByClassName) {
elements = context.getElementsByClassName(className);
if(!tagName){
return elements;
}
for(var i=0,n=elements.length; iif( selector.match(elements[i]) ){
ret.push(elements[i]);
}
}
} else {
elements = selector.find(context);
for(var i=0, n=elements.length; iif( this.match(elements[i]) ) {
ret.push(elements[i]);
}
}
}
return ret;
},
match: function(element){
var className = this.className;
var regex = new RegExp("^|\s" className "$|\s");
return regex.test(element.className);
}
};
ClassSelector.test = function (selector) {
var regex = /^([w-_] )?.([w-_] )/;
return regex.test(selector);
};
//TODO:属性选择器
function AttributeSelector(attr){
this.find = function(context){
};
this.match = function(element){
};
}
AttributeSelector.test = function (selector){
var regex = /[([w-_] )(?:=([w-_] ))?]/;
return regex.test(selector);
};
//根据父级元素过滤
function filter(parts, nodeList){
var part = parts.pop();
var selector = Factory.create(part);
var ret = [];
var parent;
for(var i=0, n=nodeList.length; iparent = nodeList[i].parentNode;
while(parent && parent !== doc){
if(selector.match(parent)){
ret.push(nodeList[i]);
break;
}
parent = parent.parentNode;
}
}
return parts[0] && ret[0] ? filter(parts, ret) : ret;
}
//根据查询选择符创建相应选择器对象
var Factory = {
create: function (query) {
if (IDSelector.test(query)) {
return new IDSelector(query);
} else if (ClassSelector.test(query)) {
return new ClassSelector(query);
} else {
return new TagSelector(query);
}
}
};
ns.dom || (ns.dom = {});
ns.dom.get = api;
}(this));