可以使用单引号、双引号、反引号来定义字符串
let single = 'single-quoted'; let double = "double-quoted"; let backticks = `backticks`;
反引号里可以嵌套表达式，表达式要以${}包裹
function sum(a, b) { return a + b; } alert(`1 + 2 = ${sum(1, 2)}.`); // 1 + 2 = 3.
此外，反引号允许字符串以多行出现
let guestList = `Guests: * John * Pete * Mary `; alert(guestList); // a list of guests, multiple lines
可以使用换行符\n
let str1 = "Hello\nWorld"; // two lines using a "newline symbol" // two lines using a normal newline and backticks let str2 = `Hello World`; alert(str1 == str2); // true
可以计算字符串长度，通过调用length属性即可
alert( `My\n`.length ); // 3
可以使用中括号的语法来访问某一个字符，或者使用charAt方法
let str = `Hello`; // the first character alert( str[0] ); // H alert( str.charAt(0) ); // H // the last character alert( str[str.length - 1] ); // o
也可以使用for of语句来迭代字符串
for (let char of "Hello") { alert(char); // H,e,l,l,o (char becomes "H", then "e", then "l" etc) }
字符串被定义后，不能单独改变某个字符
let str = 'Hi'; str[0] = 'h'; // error alert( str[0] ); // doesn't work
但是可以将值赋予一个新的字符串
let str = 'Hi'; str = 'h' + str[1]; // replace the string alert( str ); // hi
可以使用indexOf来查找字符串第一次出现的位置，如果没有找到就返回-1
let str = 'Widget with id'; alert( str.indexOf('Widget') ); // 0, because 'Widget' is found at the beginning alert( str.indexOf('widget') ); // -1, not found, the search is case-sensitive alert( str.indexOf("id") ); // 1, "id" is found at the position 1 (..idget with id)
也可以从某个位置找起，indexOf接收第二个参数，表示从哪找起
let str = 'Widget with id'; alert( str.indexOf('id', 2) ) // 12
可以使用includes来判断字符串是否存在
alert( "Widget with id".includes("Widget") ); // true alert( "Hello".includes("Bye") ); // false
可以使用startWith或者endWith来查询字符串的开头和结尾
alert( "Widget".startsWith("Wid") ); // true, "Widget" starts with "Wid" alert( "Widget".endsWith("get") ); // true, "Widget" ends with "get"
可以使用slice截取子串
let str = "stringify"; alert( str.slice(0, 5) ); // 'strin', the substring from 0 to 5 (not including 5) alert( str.slice(0, 1) ); // 's', from 0 to 1, but not including 1, so only character at 0
substring和slice差不多，不过起始位置可以比结束位置大
let str = "stringify"; // these are same for substring alert( str.substring(2, 6) ); // "ring" alert( str.substring(6, 2) ); // "ring"
substr从开始位置截取length个长度字符串
let str = "stringify"; alert( str.substr(2, 4) ); // 'ring', from the 2nd position get 4 characters
