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编写于
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@@ -1739,6 +1739,250 @@ forEach 方法会根据集合中元素的插入顺序,依次执行提供的回
has() 方法返回一个布尔值来指示对应的值 value 是否存在 Set 对象中。
### String
String 全局对象是一个用于字符串或一个字符序列的构造函数。
字符串字面量采取以下形式:
```
ts
'
string text
'
"
string text
"
"
中文/汉语
"
"
español
"
"
English
"
"
हिन्दी
"
"
العربية
"
"
português
"
"
বাংলা
"
"
русский
"
"
日本語
"
"
ਪੰਜਾਬੀ
"
"
한국어
"
```
#### 实例属性
#### length
length 属性表示一个字符串的长度。
```
ts
const
x
=
"
Mozilla
"
;
const
empty
=
""
;
console
.
log
(
"
Mozilla is
"
+
x
.
length
+
"
code units long
"
);
/* "Mozilla is 7 code units long" */
console
.
log
(
"
The empty string is has a length of
"
+
empty
.
length
);
/* "The empty string is has a length of 0" */
```
#### 实例方法
#### at
at() 方法接受一个整数值,并返回一个新的 String,该字符串由位于指定偏移量处的单个 UTF-16 码元组成。该方法允许正整数和负整数。负整数从字符串中的最后一个字符开始倒数。
```
ts
const
sentence
=
'
The quick brown fox jumps over the lazy dog.
'
;
let
index
=
5
;
console
.
log
(
`Using an index of
${
index
}
the character returned is
${
sentence
.
at
(
index
)}
`
);
// expected output: "Using an index of 5 the character returned is u"
index
=
-
4
;
console
.
log
(
`Using an index of
${
index
}
the character returned is
${
sentence
.
at
(
index
)}
`
);
// expected output: "Using an index of -4 the character returned is d"
```
#### charAt
charAt() 方法从一个字符串中返回指定的字符。
```
ts
const
anyString
=
"
Brave new world
"
;
console
.
log
(
"
The character at index 0 is '
"
+
anyString
.
charAt
(
0
)
+
"
'
"
);
// The character at index 0 is 'B'
console
.
log
(
"
The character at index 1 is '
"
+
anyString
.
charAt
(
1
)
+
"
'
"
);
// The character at index 1 is 'r'
console
.
log
(
"
The character at index 2 is '
"
+
anyString
.
charAt
(
2
)
+
"
'
"
);
// The character at index 2 is 'a'
console
.
log
(
"
The character at index 3 is '
"
+
anyString
.
charAt
(
3
)
+
"
'
"
);
// The character at index 3 is 'v'
console
.
log
(
"
The character at index 4 is '
"
+
anyString
.
charAt
(
4
)
+
"
'
"
);
// The character at index 4 is 'e'
console
.
log
(
"
The character at index 999 is '
"
+
anyString
.
charAt
(
999
)
+
"
'
"
);
// The character at index 999 is ''
```
#### charCodeAt
charCodeAt() 方法返回 0 到 65535 之间的整数,表示给定索引处的 UTF-16 代码单元
```
ts
const
sentence
=
'
The quick brown fox jumps over the lazy dog.
'
;
const
index
=
4
;
console
.
log
(
`The character code
${
sentence
.
charCodeAt
(
index
)}
is equal to
${
sentence
.
charAt
(
index
)}
`
);
// expected output: "The character code 113 is equal to q"
```
#### concat
concat() 方法将一个或多个字符串与原字符串连接合并,形成一个新的字符串并返回。
```
ts
let
hello
=
'
Hello,
'
console
.
log
(
hello
.
concat
(
'
Kevin
'
,
'
. Have a nice day.
'
))
// Hello, Kevin. Have a nice day.
```
#### endsWith
endsWith() 方法用来判断当前字符串是否是以另外一个给定的子字符串“结尾”的,根据判断结果返回 true 或 false。
```
ts
const
str1
=
'
Cats are the best!
'
;
console
.
log
(
str1
.
endsWith
(
'
best!
'
));
// expected output: true
console
.
log
(
str1
.
endsWith
(
'
best
'
,
17
));
// expected output: true
const
str2
=
'
Is this a question?
'
;
console
.
log
(
str2
.
endsWith
(
'
question
'
));
// expected output: false
```
#### includes
includes() 方法用于判断一个字符串是否包含在另一个字符串中,根据情况返回 true 或 false。
```
ts
const
str
=
'
To be, or not to be, that is the question.
'
;
console
.
log
(
str
.
includes
(
'
To be
'
));
// true
console
.
log
(
str
.
includes
(
'
question
'
));
// true
console
.
log
(
str
.
includes
(
'
nonexistent
'
));
// false
console
.
log
(
str
.
includes
(
'
To be
'
,
1
));
// false
console
.
log
(
str
.
includes
(
'
TO BE
'
));
// false
```
#### indexOf
indexOf() 方法返回调用它的 String 对象中第一次出现的指定值的索引,从 fromIndex 处进行搜索。如果未找到该值,则返回 -1。
```
ts
const
paragraph
=
'
The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?
'
;
const
searchTerm
=
'
dog
'
;
const
indexOfFirst
=
paragraph
.
indexOf
(
searchTerm
);
console
.
log
(
`The index of the first "
${
searchTerm
}
" from the beginning is
${
indexOfFirst
}
`
);
// expected output: "The index of the first "dog" from the beginning is 40"
console
.
log
(
`The index of the 2nd "
${
searchTerm
}
" is
${
paragraph
.
indexOf
(
searchTerm
,
(
indexOfFirst
+
1
))}
`
);
// expected output: "The index of the 2nd "dog" is 52"
```
#### padEnd
padEnd() 方法会用一个字符串填充当前字符串(如果需要的话则重复填充),返回填充后达到指定长度的字符串。从当前字符串的末尾(右侧)开始填充。
```
ts
const
str1
=
'
Breaded Mushrooms
'
;
console
.
log
(
str1
.
padEnd
(
25
,
'
.
'
));
// expected output: "Breaded Mushrooms........"
const
str2
=
'
200
'
;
console
.
log
(
str2
.
padEnd
(
5
));
// expected output: "200 "
```
#### padStart
padStart() 方法用另一个字符串填充当前字符串 (如果需要的话,会重复多次),以便产生的字符串达到给定的长度。从当前字符串的左侧开始填充。
```
ts
const
str1
=
'
5
'
;
console
.
log
(
str1
.
padStart
(
2
,
'
0
'
));
// expected output: "05"
```
#### repeat
repeat() 构造并返回一个新字符串,该字符串包含被连接在一起的指定数量的字符串的副本。
```
ts
"
abc
"
.
repeat
(
0
)
// ""
"
abc
"
.
repeat
(
1
)
// "abc"
"
abc
"
.
repeat
(
2
)
// "abcabc"
"
abc
"
.
repeat
(
3.5
)
// "abcabcabc" 参数 count 将会被自动转换成整数。
```
#### replace
replace() 方法返回一个由替换值(replacement)替换部分或所有的模式(pattern)匹配项后的新字符串。模式可以是一个字符串或者一个正则表达式,替换值可以是一个字符串或者一个每次匹配都要调用的回调函数。如果pattern是字符串,则仅替换第一个匹配项。原字符串不会改变。
```
ts
const
p
=
'
The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?
'
;
console
.
log
(
p
.
replace
(
'
dog
'
,
'
monkey
'
));
// expected output: "The quick brown fox jumps over the lazy monkey. If the dog reacted, was it really lazy?"
const
regex
=
/Dog/i
;
console
.
log
(
p
.
replace
(
regex
,
'
ferret
'
));
// expected output: "The quick brown fox jumps over the lazy ferret. If the dog reacted, was it really lazy?"
```
#### search
search() 方法执行正则表达式和 String 对象之间的一个搜索匹配。
```
ts
const
paragraph
=
'
The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?
'
;
// any character that is not a word character or whitespace
const
regex
=
/
[^\w\s]
/g
;
console
.
log
(
paragraph
.
search
(
regex
));
// expected output: 43
console
.
log
(
paragraph
[
paragraph
.
search
(
regex
)]);
// expected output: "."
```
#### slice
slice() 方法提取某个字符串的一部分,并返回一个新的字符串,且不会改动原字符串。
```
ts
const
str
=
'
The quick brown fox jumps over the lazy dog.
'
;
console
.
log
(
str
.
slice
(
31
));
// expected output: "the lazy dog."
console
.
log
(
str
.
slice
(
4
,
19
));
// expected output: "quick brown fox"
```
#### split
split() 方法使用指定的分隔符字符串将一个String对象分割成子字符串数组,以一个指定的分割字串来决定每个拆分的位置。
```
ts
const
str
=
'
The quick brown fox jumps over the lazy dog.
'
;
const
words
=
str
.
split
(
'
'
);
console
.
log
(
words
[
3
]);
// expected output: "fox"
const
chars
=
str
.
split
(
''
);
console
.
log
(
chars
[
8
]);
// expected output: "k"
```
#### toLowerCase
toLowerCase() 会将调用该方法的字符串值转为小写形式,并返回。
```
ts
console
.
log
(
'
中文简体 zh-CN || zh-Hans
'
.
toLowerCase
());
// 中文简体 zh-cn || zh-hans
console
.
log
(
"
ALPHABET
"
.
toLowerCase
()
);
// "alphabet"
```
#### toUpperCase
toUpperCase() 方法将调用该方法的字符串转为大写形式并返回(如果调用该方法的值不是字符串类型会被强制转换)。
```
ts
const
sentence
=
'
The quick brown fox jumps over the lazy dog.
'
;
console
.
log
(
sentence
.
toUpperCase
());
// expected output: "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG."
```
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