Javascript Syntax

Variables

Variables are containers for storing data (values).

In this example, x, y, and z, are variables, declared with the var keyword:

From the example above, you can expect:

• x stores the value 5
• y stores the value 6
• z stores the value 11

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Much Like Algebra

In this example, price1, price2, and total, are variables:

In the program, as in algebra, we use variables (such as number1) to capture values.

In the program, as in algebra, we use variables in definitions (total = price1 + price2).

From the example above, you can count to 11.

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JavaScript Identifiers

All JavaScript variables must be identified with unique names.

These unique names are called identifiers.

Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).

The general rules for constructing names for variables (unique identifiers) are:

• Names can contain letters, digits, undersers, and dollar symbols.
• Names must start with a letter
• Names can also be started in $ and _ (but we will not use it in this course)
• Sensitive words (y and Y are different)
• Reserved words (like JavaScript keywords) cannot be used as words

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The Assignment Operator

In JavaScript, the equal sign (=) is an "assignment" operator, not an "equal to" operator.

This is different from algebra. The following does not make sense in algebra:

In JavaScript, however, it makes perfect sense: it assigns the value of x + 5 to x.

(It calculates the value of x + 5 and puts the result into x. The value of x is incremented by 5.)

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JavaScript Data Types

JavaScript variables can hold up to 100 numbers and text values ​​such as "John" Doe ".

In the application, text values ​​are called text strings.

JavaScript can handle many types of data, but for now, consider numbers and strings.

Ropes are written within two or more dimensions. Numbers are written without measurements.

If you enter a number in the ratings, it will be treated as a unit of text.

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Declaring (Creating) JavaScript Variables

Creating a variable in JavaScript is called "declaring" a variable.

You declare a JavaScript variable with the var keyword:

After the declaration, the variable has no value (technically it has the value of undefined).

To assign a value to the variable, use the equal sign:

You can also assign a value to the variable when you declare it:

In the example below, we create a variable called carName and assign the value "Volvo" to it.

Then we "output" the value inside an HTML paragraph with id="demo":

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