1. Placing scripts at the bottom of the <body> element improves the display speed, because script compilation slows down the display.

2. External scripts cannot contain <script> tags.

3. JavaScript uses the var keyword to declare variables.

4. All JavaScript identifiers are case sensitive.

5. In javaScript,you can declare many variables in one statement.

E.g. var person = "John Doe", carName = "Volvo", price = 200;

6. A variable declared without a value will have the value undefined.

7. If you re-declare a JavaScript variable, it will not lose its value.

8. If you put a number in quotes, the rest of the numbers will be treated as strings, and concatenated.

E.g. var x = "5" + 2 + 3;

Here, x stores the value 523.

9. JavaScript evaluates expressions from left to right.

10. In JS, arrays are defined as:

E.g. var cars = ["Saab", "Volvo", "BMW"];

Array indexes are zero-based, which means the first item is [0], second is [1], and so on.

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Javascript notes for better understanding.