Notes on JavaScript language structure (1)_Basic knowledge

1: js supports Unicode character set, so you can name functions in Chinese.

Two: js has no initialized variables in Var, the default is undefined

Third: For variables that are neither declared nor assigned a value, if used directly, a system-level Error will be thrown. If you use typeof (typeof is a type operator) operation, regardless of whether it has been declared, a string "undefined" will be returned;

Example:

//a Undeclared

alert(typeof(a));//undefined

alert(a);//Error

Four: Arithmetic operators. " " can be used to convert a value into a string more conveniently. The specific operation is to add an empty string to the value (or not write it).

Example:

Var a=2.96;

Var b=1.0;

Alert(a ”” b);//Get the string” 2.961"

Use "-" to convert a string into a numerical value. The specific operation is to subtract a value 0 from this string

Var a="2.96";

alert(a 1);//Get the string "2.961" (force the value into a string)

alert(a-0 1);//Get the value 3.96

The following is an example I made: