> MOSE ## History of JavaScript JavaScript was created at Netscape Communications ****by Brendan Eich in 1995. Netscape and Brendan Eich designed JavaScript as a scripting language for Netscape Navigator which was a leading web browser in the 1990s. JavaScript's first name was Mocha. After that, it was known as Live Script and later known as JavaScript. ## JavaScript placement - JavaScript can be placed in a html file in the body section using a script tag and placing you JavaScript code within the tags. ```

This is web page body

``` - Can also be placed in an external file source with an extension ".js" e.g **filename.js** then include it in a html code using **script** tag and **src **attribute ``` ....... ``` ## JavaScript Variables - JavaScript has variables that you can declare with the optional var keyword.`var age="21years"` - JavaScript variable shouldn't start with numbers but with letters or underscore. i.e can be declared as `_name="Moses"` and `name="Moses"` but **not **`1name="Moses"` which is an invalid variable - They are case sensitive. i.e `Name` and `name` are two different variables. - Don`t use reserved words as variables NB: ## Operators let's declare variables `A = 10 B = 20` **1. +(Addition)** Adds two operands. Ex: ` result = a + b; document.write("a + b = "); document.write(result); ` will give `a + b = 43` **NOW TRY USING THE OTHER OPERATORS** **2. -(Subtraction)** Subtracts the second operand from the first Ex: A - B will give -10 **3. *(Multiplication)** Multiply both operands Ex: A * B will give 200 **4. / (Division)** Divide the numerator by the denominator Ex: B / A will give 2 **5. % (Modulus)** Outputs the remainder of an integer division Ex: B % A will give 0 **6. ++ (Increment)** Increases an integer value by one Ex: A++ will give 11 **7. -- (Decrement)** Decreases an integer value by one Ex: A-- will give 9 ## Comparison Operetors A = 10 B = 20 **1. == (Equal**) Checks if the value of two operands are equal or not, if yes, then the condition becomes true. Ex: `result = (a == b); document.write("(a == b) => "); document.write(result);` THE OUTPUT FOR THE CODE WILL BE `(a == b) => false` **2. != (Not Equal)** Checks if the value of two operands are equal or not, if the values are not equal, then the condition becomes true. Ex: (A != B) is true. **3. > (Greater than)** Checks if the value of the left operand is greater than the value of the right operand, if yes, then the condition becomes true. Ex: (A > B) is not true. **4. < (Less than)** Checks if the value of the left operand is less than the value of the right operand, if yes, then the condition becomes true. Ex: (A < B) is true. **5. >= (Greater than or Equal to)** Checks if the value of the left operand is greater than or equal to the value of the right operand, if yes, then the condition becomes true. Ex: (A >= B) is not true. **6. <= (Less than or Equal to)** Checks if the value of the left operand is less than or equal to the value of the right operand, if yes, then the condition becomes true. Ex: (A <= B) is true. ## Conditional statements ## if else statement The ‘if’ statement is the fundamental control statement that allows JavaScript to make decisions and execute statements conditionally. **syntax** ` ``` if (expression){ Statement(s) to be executed if expression is true }else{ Statement(s) to be executed if expression is false } ``` Example ```

Try using a different variable value

``` **Output** `You are not qualified to enter the site. Set the variable to a different value and ten try... ` ** ## else if statement else if statement allows JavaScript to make a correct decision out of several conditions. **syntax** ``` if (expression 1){ Statement(s) to be executed if expression 1 is true }else if (expression 2){ Statement(s) to be executed if expression 2 is true }else if (expression 3){ Statement(s) to be executed if expression 3 is true }else{ Statement(s) to be executed if no expression is true } ``` Example ```

Try using a different variable value

``` output ` The Outpost Try using a different variable value `

pharaoh_ke

introduction to Javascript

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