# String

Some of the basic string methods you must familiar with in your programming languages.

* Position, Index, Search
  * Beginning of character.
  * String replace without regular expression.
  * For example :

    ```
    var fruitString = "Apple, Banana,Orange";
    if (fruitString.indexOf("Apple") > 0) {
    console.log("Apple is here");
    }
    ```

    or 

    \`\`\`

    var fruitString = "Apple, Banana,Orange";

    if (fruitString.indexOf("Apple") != -1) {

    console.log("Apple is here");

    }
* Comparison
  * equal
  * In general, that is ==.
  * object comparison, In java, use like

    ```
    a.equals(b)
    ```
* Length
  * Declaration blank or null :

    Be careful to declare a string.

    In C, string is immutable.

    But in the modern languages, java, js, python, go, string can be changed.
  * Is String empty? How to check if string is empty? Use length, but just need to make sure not null first.

    ```
    if (str != null && str.length > 0) {

    }
    ```
* Token Parser
  * Repetitive pattern match
  * Parse to array
  * For example: parse the following string to array:

    ```
    var fruitString = "Apple, Banana,Orange";
    var fruits = fruitString.split(",");
    ```
* Convert
  * String to Number
  * In the web page data submission, those data are just string. Any particular ID need to convert to integer or long.
  * For example :

    ```javascript
    var a = "123";
    var i = parseInt(a, 10);
    ```

    ```python
    a = "123"
    i = int(a)
    ```
* Join string

  * Join string array in a string.
  * It's considering to be better performance than string appending.
  * For example :

    \`\`\`

    var fruits = \["Apple", "Banana", "Orange"];

    var fruitString = fruits.join(", ");

  ```
  * String appending is not the best practice.
  ```

  var fruits = \["Apple", "Banana", "Orange"]; var fruitString = ""; furitString += fruits\[0] + ", "; furitString += fruits\[1] + ", "; furitString += fruits\[2] + ", ";

  \`\`\`
* Remove extra spacing

  * Remove leading spacing.
  * Remove trailing spacing".
  * For example :

    \`\`\`

    var name = "  John Doe ";

    name = name.trim();

  \`\`\`
* To uppercase, lowercase.
  * Most use in case insensitive search pattern match and case insensitive search order.
* Regular Expression
  * For pattern match.
  * String replacement.
  * For example : remove line break.
    * [Online regular expression match](https://www.debuggex.com/)
    * Look around extension (lookahead, lookbehind)