Methods in Arrays – Part 2

Arrays topic in TypeScript is divided into following parts:

• Introduction to Arrays
• Array Objects
• Methods in Arrays – Part 1
• Methods in Arrays – Part 2
• Methods in Arrays – Part 3
• Multidimensional Arrays
• Arrays in functions

Below are the methods that are discussed in this section

lastIndexOf	map	pop
push	reduce	reduceRight

lastIndexOf

This method returns the last index at which an element can be found. It will return -1 if the element is not found.
– Returns the last index of the element.
– element: this is the element that we are searching in the array
– fromIndex: Index from which we need to start searching backwards. This is optional.
Syntax

arrayName.lastIndexOf(element, [fromIndex]);

Below is a sample code

var users:string[] = ["Akanksha","Anita", "Aarav","Apoorv","Anita","Raj"];
console.log("Original Array: " + users);
console.log(users.lastIndexOf("Anita"));
console.log(users.lastIndexOf("Anil"));

Below is the output of above code

map

This method creates a new array with the results of calling a function on every element in the array.
Syntax

arrayName.map(function);

Below is a sample code

var starter = [10,20,30];
function multiplyByFive (val, index, arr) {
    return val * 5;
}
var result = starter.map(multiplyByFive);
console.log(result);

Below is the output of above code

pop

This method removes the last element of the array and returns it.
Syntax

arrayName.pop();

Below is a sample code

var nums:number[] = [10,20,30];
console.log("Original array: " + nums);
console.log("Removing last element: " + nums.pop());
console.log("Modified array: " + nums);

Below is the output of above code

push

This method adds a new element at the end of the array and returns the length of the array.
Syntax

arrayName.push(element1, element2, .....);

Below is an example

var nums:number[] = [10,20,30];
console.log("Original array: " + nums);
console.log("New length of the array: " + nums.push(40,50));
console.log("Modified array: " + nums);

Below is the output of above code

reduce

This method applies a function simultaneously against two values of an array, from left to right, to reduce the array to a single value.
Syntax

array.reduce(function);

Below is an example

var nums:number[] = [10,20,3];
function multiply(a:number, b:number):number{
    return (a*b);
}
console.log(nums.reduce(multiply));

In the above example, it will first multiply 10 with 20. This will give 200. Then it will multiply 200 with 3, resulting in 600. That is, it will perform the operation in left to right direction.
Below is the output of above code

reduceRight

This method applies a function simultaneously against two values of an array, from right to left, to reduce the array to a single value.
Syntax

array.reduceRight(function);

Below is an example

var nums:number[] = [10,20,300];
function subtract(a:number, b:number):number{
    return (a-b);
}
console.log(nums.reduceRight(subtract));

In this example, first it will subtract 20 from 300, which will return 280. Then it will subtract 10 from 280, resulting in 270. That is, it will perform the operation in right to left direction.
Below is the output of above code

Strings in TypeScript – Part 2

Strings in TypeScript is divided in three parts:

• Part 1
• Part 2. This is Part 2
• Part 3

This section has the details of following methods:

subString	subStr	split
slice	search	replace
match	localeCompare	lastIndexOf

lastIndexOf()

This method returns the last index of a specified value within a string. Search will start from the starting of the string. variable is the string in which we are searching for the value.
– searchString is the value which we are searching in the variable.
– fromIndex is an integer which specify the starting index for the search. It will return -1 if the string is not found.
Syntax

variable.lastIndexOf(searchString, [fromIndex])

Below is a sample code

var str1 = new String("This is a sample string sample");
console.log("Last Index of i: " + str1.lastIndexOf('i'));
console.log("Last Index of is: " + str1.lastIndexOf("is"));
console.log("Last Index of sample: " + str1.lastIndexOf("sample"));
console.log("Last Index of sample: " + str1.lastIndexOf("sample", 14));
console.log("Last Index of two: " + str1.lastIndexOf("two"));

Below is the output of above code

localeCompare()

This method will return an integer value after sorting two strings
Syntax

str1.localeCompare(str2);

– Returns 0 if str1 and str2 are equal.
– Returns 1 if str2 comes before str1 in the locale sort order.
– Returns -1 if str2 comes after str1 in locale sort order.

Below is an example

var str1 = new String("ab");
var str2 = new String("cd");    
var index1 = str1.localeCompare("ab");  
var index2 = str2.localeCompare("ab");  
var index3 = str1.localeCompare("cd"); 
console.log("Perfect Match: " + index1 );
console.log("Parameter value comes before the string value: " + index2 );
console.log("Parameter value comes after the string value: " + index3 );

Below is the output of above code

match()

This method searches a string for a match against a regular expression. This will return an array of all matches. Include g modifier to do a global search, that is in complete string. Otherwise it will return only the first match in the string. i is used to match without case-comparison. This method will return null if no match is found.
Syntax

variable.match(regexpre);

Below is an example

var str1 = new String("This is an example. ThiS IS good.");
console.log(str1.match(/is/g));
console.log(str1.match(/is/gi));

Below is the output of above code

replace

This method first finds a match between a regular expression and a string, then replaces the matched substring with another substring.
Syntax

variable.replace(regexp, substring);

Below is a sample code

var str1 = new String("I like to eat mangoes, but mangoes only come in summers. Mangoes are yellow in color.");
var result = str1.replace(/mangoes/gi,"apples");
console.log(result);

Below is the output of above code

search()

This method searches a substring, using a regular expression, within a string and returns the index.
If the regular expression is not inside the string, it will return -1.
Syntax

string.search(regexp);

Below is a sample code

var str1 = new String("I like to eat mangoes, but mangoes only come in summers. Mangoes are yellow in color.");
var index = str1.search(/mangoes/gi);
console.log("First index of mangoes: " + index);

Below is the output of above code

slice()

This method extracts a section of a string and returns a new string. You can remove characters from beginning as well as from the end of the string. Giving the value fromEnd is optional.
Syntax

string.slice(fromBeginning, [fromEnd]);

Below is an example

var str1 = new String("I like to eat mangoes, but mangoes only come in summers.");
console.log(str1.slice(4,-5));

Below is the output of above code

split

This will split a string into array based on a substring. This method returns an array.
– separator is the substring used to split a string.
– limitOfValues is an integer value that tells how many values to return.
Syntax

string.spli(separator, [limitOfValues])

Below is an example

var str1 = new String("red,orange,blue,black,yellow,green");
var colors = str1.split(',');
var i:number;
console.log("All color values");
for(i=0; i<colors.length; i++)
{
    console.log(colors[i]);
}
var colors1 = str1.split(',',3);
var i:number;
console.log("\nOnly 3 color values");
for(i=0; i&lt;colors1.length; i++)
{
    console.log(colors1[i]);
}

Below is the output of above code

substr()

This method will return a new string.
– startIndex represents the index from where we want to start extracting the substring.
– length is a number representing the number of characters we want to extract. This is optional.
Syntax

string.substr(startIndex, [length]);

Below is a an example

var str1 = new String("I like to eat mangoes, which are yellow in color");
console.log("Original String: " + str1);
console.log("(0): " + str1.substr(0));
console.log("(4): " + str1.substr(4));
console.log("(5,9): " + str1.substr(5,9));
console.log("(-2): " + str1.substr(-2));
console.log("(-5,4):" + str1.substr(-5,4));

Below is the output of above code

substring()

This method will return a new string between two indexes. It does not take negative values like we used in substr() method, hence we cannot start extraction from the end of the string.
– startIndex is the starting index from where the extraction should begin
– endIndex is the index where the extraction should end. This is optional.
Syntax

string.substring(startIndex,[endIndex]);

Below is an example

var str1 = new String("I like to eat mangoes, which are yellow in color");
console.log("Original String: " + str1);
console.log("(0): " + str1.substring(0));
console.log("(4): " + str1.substring(4));
console.log("(5,9): " + str1.substring(5,9));
console.log("(-2): " + str1.substring(-2));
console.log("(-5,4): " + str1.substring(-5,4));

Below is the output of the above code