on 19-May-2017 (Fri)

For all w ∈ W, A ∈ L , t ∈ T : V (2 t A, w) = 1 ↔ ∀v ∈ V (t, w) : V (A, v) = 1 ◦ For all w ∈ W, A ∈ L , t ∈ T : V (3 t A, w) = 1 ↔ ∃v ∈ V (t, w) : V (A, v) = 1

V on T : ◦ For all w ∈ W, X ⊆ W : V (k X , w) = X ◦ For all w ∈ W, t ∈ T , A ∈ L : V ((t ∗ A), w) = min 6 V (t,w) ({v ∈ W |V (v, A) = 1})

The String global object is a constructor for strings, or a sequence of characters.

Unlike some other languages, JavaScript makes no distinction between single-quoted strings and double-quoted strings; therefore, the escape sequences above work in strings created with either single or double quotes.

You can use the + operator to append multiple strings together, like this:

Escape notation

Beside regular, printable characters, special characters can be encoded using escape notation:

Code	Output
\0	the NULL character
\'	single quote
\"	double quote
\\	backslash
\n	new line
\r	carriage return
\v	vertical tab
\t	tab
\b	backspace
\f	form feed

Or you can use the backslash character ("\") at the end of each line to indicate that the string will continue on the next line. Make sure there is no space or any other character after the backslash (except for a line break), or as an indent; otherwise it will not work. That form looks like this:

 let longString = "This is a very long string which needs \
to wrap across multiple lines because \
otherwise my code is unreadable." ; 

Strings are useful for holding data that can be represented in text form. Some of the most-used operations on strings are to check their length, to build and concatenate them using the + and += string operators, checking for the existence or location of substrings with the indexOf() method, or extracting substrings with the substring() method.

Some of the most-used operations on strings are to check their length ,

There are two ways to access an individual character in a string. The first is the charAt() method:

 return 'cat' . charAt ( 1 ) ; // returns "a" 

The other way to access an individual character on a screen is to treat the string as an array-like object, where individual characters correspond to a numerical index:

 return 'cat' [ 1 ] ; // returns "a" 

return 'cat' [ 1 ] ; // returns "a"

C developers have the strcmp() function for comparing strings. In JavaScript, you just use the less-than and greater-than operators:

 var a = 'a' ; var b = 'b' ; if ( a < b ) { // true console . log ( a + ' is less than ' + b ) ; } else if ( a > b ) { console . log ( a + ' is greater than ' + b ) ; } else { console . log ( a + ' and ' + b + ' are equal.' ) ; } 

String literals (denoted by double or single quotes) and strings returned from String calls in a non-constructor context (i.e., without using the new keyword) are primitive strings

JavaScript automatically converts primitives to String objects, so that it's possible to use String object methods for primitive strings

String literals (denoted by double or single quotes) and strings returned from String calls in a non-constructor context (i.e., without using the new keyword)

JavaScript automatically converts primitives to String objects, so that it's possible to use String object methods for primitive strings

In contexts where a method is to be invoked on a primitive string or a property lookup occurs, JavaScript will automatically wrap the string primitive and call the method or perform the property lookup.

 var s_prim = 'foo' ; 
 var s_obj = new String ( s_prim ) ;
 console . log ( typeof s_prim ) ; // Logs "string"
 console . log ( typeof s_obj ) ; // Logs "object" 

String primitives and String objects also give different results when using eval(). Primitives passed to eval are treated as source code; String objects are treated as all other objects are, by returning the object. For example:

 var s1 = '2 + 2' ; // creates a string primitive var s2 = new String ( '2 + 2' ) ; // creates a String object console . log ( eval ( s1 ) ) ; // returns the number 4 console . log ( eval ( s2 ) ) ; // returns the string "2 + 2" 

String primitives and String objects also give different results when using eval() . Primitives passed to eval are treated as source code; String objects are treated as all other objects are, by returning the object. For example:

For these reasons, code may break when it encounters String objects when it expects a primitive string instead,

For these reasons, code may break when it encounters String objects when it expects a primitive string instead,

A String object can always be converted to its primitive counterpart with the valueOf() method.

In this article, I’ll explain how to solve freeCodeCamp’s “Repeat a string repeat a string” challenge. This involves repeating a string a certain number of times.

There are the three approaches I’ll cover:

1. using a while loop
2. using recursion
3. using ES6 repeat() method

A while statement executes its statement as long as a specified condition evaluates to true.

A while statement looks like this:

while (condition)
 statement

A while statement looks like this:

while (condition)
 statement

with a condition which is evaluated before each pass through the loop. If the condition is true, the statement is executed. If the condition is false, the execution continues with any statement after the while loop.

The statement is executed as long as the condition is true. Here’s the solution:

Recursion is a technique for iterating over an operation by having a function call itself repeatedly until it arrives at a result. There are a few key features of recursion that must be included in order for it to work properly.

• The first is a base case: this is a statement, usually within a conditional clause like if, that stops the recursion.
• The second is a recursive case: this is the statement where the recursive function is called on itself.

You can use a ternary operator as a shortcut for the if/else statement, like this:

times > 0 ? string.repeat(times) : "";

This can be read as:

if (times > 0) { 
 return string.repeat(times);
} else {
 return "";
}

Approach #3: Repeat a String using ES6 repeat() method

For this solution, you’ll use the String.prototype.repeat() method:

• The repeat() method constructs and returns a new string which contains the specified number of copies of the string on which it was called, concatenated together.

You can use a ternary operator as a shortcut for the if/else statement, like this:

times > 0 ? string.repeat(times) : "";