JavaScript不只是簡單的構建塊
JavaScript對象、基本類型和字面值之間的區別
對象：Object windwow 數組、正則、日期、原型、使用 new 通過構造方法創建的
基本類型：字符串、數值、布爾類型、null和undefined，只有字符串、數組和布爾值有構造函數，其餘兩種都是字面值
字面值
var str1 = "this is a simple string";
var num1 = 1.45;
var answer = true;當你使用嚴格相等性來比較一個對象示例和一個字面值的時候，可以快速區分出一個基本類型和一個對象實例：即基本類型變量嚴格地等於字面值
var str1 = String("string");
var num1 = Number(1.45);
var bool1 = Boolean(true);
if(str1 ==="string")
console.log('equal');
if(num1 === 1.45)
console.log('equal');
if(bool1 === true)
console.log('equal');
var str2 = new String("string");
var num2 = new Number(1.45);
var bool2 = new Boolean(true);
if(str2 ==="string")
console.log('equal');
else console.log('not equal');
if(num2 === 1.45)
console.log('equal');
else console.log('not equal');
if(bool2 === true)
console.log('equal');
else console.log('not equal');
輸出：
"equal"
"equal"
"equal"
"not equal"
"not equal"
"not equal"從字符串提取出一個列表
1 使用 trim去掉多餘的空格
2 使用正則表達式去掉多餘的空格
var sentence = 'This is one sentence.This is a sentence with a list of items:'+
'cherries , oranges , apples,bananas.That was the list of lists.';
var start = sentence.indexOf(':');
var end = sentence.indexOf('.',start+1);
var listStr = sentence.substring(start+1,end);
var fruits = listStr.split(',');
fruits.forEach(function(elem,index,array){
array[index] = elem.trim();
});
var fruits2 = listStr.split(/\s*,\s*/);
console.log(fruits);
console.log(fruits2);檢查一個存在的、非空的字符串
//var unknownVairable = new String("string");
var unknownVairable = "string";
if(((typeof unknownVairable != 'undefined' && unknownVairable) && unknownVairable.length > 0) && typeof unknownVairable.valueOf()=='string'){
console.log(true);
}插入特殊的字符
解決方案：使用轉義序列，例如要想添加到頁面的一段文本中添加一個版權符號
轉義序列最重要的用法之一，是在雙引號或單引號分隔開的字符串中，包含雙引號或單引號：
var newString = 'you can\'t use single quotes '+
'in a string surrounded by single quotes.'+
'Oh,wait a sec... yes you can.';
console.log(newString);
輸出：
"you can't use single quotes in a string surrounded by single quotes.Oh,wait a sec... yes you can."找到並突出顯示一個模式的所有實例
var searchString = "Now is the time and this is the time and that is the time";
var pattern = /t\w*e/g;
var matchArray;
var str = "";
while((matchArray = pattern.exec(searchString))!=null){
str+= "at "+ matchArray.index+" we found "+ matchArray[0] +"\n";
}
console.log(str);
輸出：
"ime";
var pattern = /t\w*e/g;
var matchArray;
var str = "";
while((matchArray = pattern.exec(searchString))!=null){
str+= "at "+ matchArray.index+" we found "+ matchArray[0] +"\n";
}
console.log(str);
var re = /a(p+).*(pie)/ig;//全局標誌，觸發了RegExp對象去保留每一次匹配的位置，並且從之前找到的匹配之後開始搜索。
var result = re.exec("The apples in the apple pie are tart");
console.log(result);
console.log(result.index);
console.log(result.input);
Console Run Clear
"at 7 we found the
at 11 we found time
at 28 we found the
at 32 we found time
at 49 we found the
at 53 we found time
"
var re = /a(p+).*(pie)/ig;
var result = re.exec("The apples in the apple pie are tart");
console.log(result);
console.log(result.index);
console.log(result.input);
輸出：
["apples in the apple pie", "pp", "pie"]
4
"The apples in the apple pie are tart"使用exec和全局標誌來查找並突出顯示一個文字字符串中的所有匹配
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>Searching for strings</title>
<style type="text/css">
.found{
background-color: #ff0;
}
</style>
</head>
<body>
<form id="textsearch">
<textarea name="" id="incoming" cols="150" rows="10"></textarea>
<p>Search pattern:<input type="text" id="pattern" name=""></p>
</form>
<button id="searchSubmit">Search for pattern</button>
<div id="searchResult"></div>
<script type="text/javascript">
window.onload= function(){
document.getElementById("searchSubmit").onclick = function(){
//獲取模式
var pattern = document.getElementById("pattern").value;
var re = new RegExp(pattern, "g");
//獲取字符串
var searchString = document.getElementById("incoming").value;
var matchArray;
var resultString ="<pre>";
var first = 0;
var last = 0;
while((matchArray = re.exec(searchString))!=null){
last = matchArray.index;
//獲取所有匹配的字符串，將其連接起來
resultString += searchString.substring(first, last);
//使用class，添加匹配的字符串
resultString +="<span class='found'>"+matchArray[0]+"</span>";
first = re.lastIndex;
}
//完成字符串
resultString += searchString.substring(first,searchString.length);
resultString +="</pre>";
//插入到頁面
document.getElementById("searchResult").innerHTML = resultString;
}
};
</script>
</body>
</html>
