In Javascript Single Threaded?

Now, JavaScript is a single-threaded language, which means it has only one call stack that is used to execute the program. The call stack is the same as the stack data structure that you might read in Data structures.

Is JavaScript multi threaded?

No, JavaScript is not multi-threaded. It is event driven and your assumption of the events firing sequentially (assuming they load sequentially) is what you will see.

What is meant by single threaded language?

A single-thread language is one with a single call stack and a single memory heap. It means that it runs only one thing at a time. A stack is a continuous region of memory, allocating local context for each executed function.