JavaScript variables are containers for storing data values.
In this example, x, y, and z, are variables:
From the example above, you can expect:
In this example, price1, price2, and total, are variables:
In programming, just like in algebra, we use variables (like price1) to hold values.
In programming, just like in algebra, we use variables in expressions (total = price1 + price2).
From the example above, you can calculate the total to be 11.00
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JavaScript variables are containers for storing data values. |
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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:
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JavaScript identifiers are case-sensitive. |
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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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The "equal to" operator is written like == in JavaScript. |
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JavaScript variables can hold numbers like 100, and text values like "John Doe".
In programming, text values are called text strings.
JavaScript can handle many types of data, but for now, just think of numbers and strings.
Strings are written inside double or single quotes. Numbers are written without quotes.
If you put quotes around a number, it will be treated as a text string.
Creating a variable in JavaScript is called "declaring" a variable.
You declare a JavaScript variable with the var keyword:
After the declaration, the variable is empty (it has no value).
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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It's a good programming practice to declare all variables at the beginning of a script. |
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You can declare many variables in one statement.
Start the statement with var and separate the variables by comma:
A declaration can span multiple lines:
In computer programs, variables are often declared without a value. The value can be something that has to be calculated, or something that will be provided later, like user input.
A variable declared without a value will have the value undefined.
The variable carName will have the value undefined after the execution of this statement:
If you re-declare a JavaScript variable, it will not lose its value.
The variable carName will still have the value "Volvo" after the execution of these statements:
As with algebra, you can do arithmetic with JavaScript variables, using operators like = and +:
You can also add strings, but strings will be concatenated (added end-to-end):
Also try this:
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If you add a number to a string, the number will be treated as string, and concatenated. |
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