Javascript-9-datatype String

 String

A string variable can be defined with " ' " or  " "" " as below:

• var carname = "Volvo XC60";(recommended)
• var y = new String("John");(not recommended as it takes more processing time in comparison)

A string variable size can be measure as:

• var carname = "Volvo XC60";(recommended)
• carname.length;(not recommended as it takes more processing time in comparison)

==  and  === operators on strings in below scenarios:

• var x = "John";             
• var y = new String("John");
• var z = new String("John");

(x==y) //returns true

(x===y) //returns false (since string and object)

(y==z) //returns false

(y===z) //returns false

\ escape character.

\can be used prior to special characters within a string.

• var x = 'It\'s alright';
• var y = "We are the so-called \"Vikings\" from the north."

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Breaking a long code line

1)the best place to break it is after an operator: 

• document.getElementById("demo").innerHTML =
  "Hello Dolly.";

2)within a text string with a single backslash"\" 

• document.getElementById("demo").innerHTML ="Hello \
  Dolly.";
• document.getElementById("demo").innerHTML = \ 
  "Hello Dolly!"; // WRONG

3)the best way is, use string addition: 

• document.getElementById("demo").innerHTML = "Hello" + 
  "Dolly!";

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Finding a String in a String

Let's say,

var str = "Please locate where 'locate' occurs!";

•  indexOf() : returns the first index of the first occurrence of the string
• var pos = str.indexOf("locate"); 
• //returns 7

• lastIndexOf() method returns the index of the last occurrence
• var pos = str.lastIndexOf("locate");
• //returns 21

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Searching a String in a String

Let's say,

var str = "Please locate where 'locate' occurs!";

•  search() method searches a string for a specified value and returns the position of the match
• var pos = str.search("locate"); //returns 7. 
• similar to indexOf()

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Extracting String Parts

Let's say,

var str = "Apple, Banana, Kiwi";

There are 3 methods for extracting a part of a string:

• slice(start index, end index): slice() extracts a part of a string and returns the extracted part in a new string.

• var res = str.slice(7, 13); //returns Banana
• var res = str.slice(-12, -6);//the position is counted from backward index. returns Banana
• var res = str.slice(7); //returns Banana, Kiwi
• var res = str.slice(-12); //returns Banana, Kiwi

• substring(start index, end): similar to slice(). does not accept -ve index
• var res = str.substring(7, 13); //returns Banana

• substr(start index, length): substr() is similar to slice(), but second parameter is the length instead of end-index. Accepts -ve index.
• var res = str.substr(7, 9);//returns Banana K

Extracting String Characters

Let's say,

var str = "Hello World";

There are 2 safe methods for extracting string characters:

• charAt(position): 
• str.charAt(0); // returns H

• charCodeAt(position). returns the unicode of the character
• str.charCodeAt(0);// returns 72

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Replacing String Content(replace(str2replace,replacedWith))

Lets say,

str = "Please Microsoft visit Microsoft!";

• var n = str.replace("Microsoft", "W3Schools");//replace all "Microsoft" occurence
• var n = str.replace(/Microsoft/g, "W3Schools");//replace only the first Microsoft occurence

To replace all matches, use a regular expression with a g flag (for global match):

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Converting to Upper and Lower Case

Lets say,

var text1 = "Hello World!";       // String

• var text2 = text1.toUpperCase(); //returns HELLO WORLD
• var text2 = text1.toLowerCase(); //returns hello world

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Converting a String to an Array

Lets say, var txt = "a,b,c,d,e";  

• txt.split(",");          // Split on commas and returns array
• txt.split(" ");          // Split on spaces and returns array
• txt.split("|");          // Split on pipe and returns array
• However,  txt.split(""); // Split in characters. i.e array of characters

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Other methods:

• concat() joins two or more strings: 
• var text1 = "Hello";
  var text2 = "World";
  text3 = text1.concat(" ", text2); //Returns Hello World!
• var text = "Hello" + " " + "World!";
  var text = "Hello".concat(" ", "World!");//Returns Hello World!
• str.match(regex) : returns the string based on regex
• var text1 = "Hello World new world";
  text3 = text1.match(/world/); //Returns World!
• str.repeat(NumberOfTimesToRepeat'str') : 
• str.repeat(3);//Returns Hello World! Hello World! Hello World!

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String.prototype.replace()

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace

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