```dart
// Check whether a string contains another string.
assert('Never odd or even'.contains('odd'));

// Does a string start with another string?
assert('Never odd or even'.startsWith('Never'));

// Does a string end with another string?
assert('Never odd or even'.endsWith('even'));

// Find the location of a string inside a string.
assert('Never odd or even'.indexOf('odd') == 6);
```


dart.md

```go
// 前缀
func HasPrefix(s, prefix string) bool {
    return len(s) >= len(prefix) && s[:len(prefix)] == prefix
}

// 后缀
func HasSuffix(s, suffix string) bool {
    return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
}

// 子串
func Contains(s, substr string) bool {
    for i := 0; i < len(s); i++ {
        if HasPrefix(s[i:], substr) {
            return true
        }
    }
    return false
}
```


go.md

```js
let s = "Hello world!";
s.startsWith("Hello"); // true
s.endsWith("!"); // true
s.includes("o"); // true

let s = "Hello world!";
s.startsWith("world", 6); // true
s.endsWith("Hello", 5); // true
s.includes("Hello", 6); // false

"hello world".indexOf("o"); // 4
"JavaScript".indexOf("script"); // -1
"hello world".indexOf("o", 6); // 7

"hello world".lastIndexOf("o"); // 7
"hello world".lastIndexOf("o", 6); // 4

"cat, bat, sat, fat".search("at"); // 1
// replace方法用于替换匹配的子字符串，一般情况下只替换第一个匹配（除非使用带有g修饰符的正则表达式）。
"aaa".replace("a", "b"); // "baa"

// 2 is in the string
if ("123".includes("2")) {
  console.log("2 is in the string");
}

// 2 is not in the string
if (!"456".includes("2")) {
  console.log("2 is not in the string");
}

// Has a number
if ("iphone 8".match(/\d/g)) {
  console.log("Has a number");
}

// Doesn't have a number
if (!"iphone x".match(/\d/g)) {
  console.log("Doesn't have a number");
}
```


js.md

```python
# 2 is in the string
if "2" in "123":
    print("2 is in the string")

# 2 is not in the string
if "2" not in "456":
    print("2 is not in the string")


import re

# Has a number
if re.search(r"\d", "iphone 8"):
    print("Has a number")

# Doesn't have a number
if not re.search(r"\d", "iphone x"):
    print("Doesn't have a number")
```


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