The data types in js are all weakly typed. Weak typing means that the data itself has no type, and it is what type you give it. Var is an inference keyword, which means that I don't want to know what type of data is. I can infer the data type by giving you a value. For example: var aa =123; Then aa is an integer type, and var aa =“ABC ". Similarly, aa is also a string type. The key is to see what kind of data you assign.