1, what is JS Object-based and event-driven and has a relatively secure client-side scripting language, developed by Netscape. 2, JS data type 1, basic data type undefined,null,number,boolean,string, 3, value that can be converted to false 0, empty string, NULL, False,undefined 4, value that can be converted to true non-empty string, true, non-0 digit, obj 5, display conversion, and hermit conversion Display conversion: Boolean number string implicit conversion: 1, when a string and a number for the + operation, the value is converted to a string 2, in addition to the + operation, The remaining arithmetic operations are converting a string to a numeric value 3, a comparison between strings, a bitwise comparison of ASCII values of characters 4, string and numeric comparisons, the string is converted to numeric 6, Nan nan is not converted to any numeric value, and is converted to false not equal to any values 7, some special uses of logical operations var A = 0| | 5;console.log (a)///Print value 5, when or when the first implicit conversion to a Boolean value is False, the output is the second number var B = 5| | 0;console.log (b);//Print value 5, when or when the first hermit is converted to a Boolean value of true, the output is the first number 8, the self-increment 1, a++: First use after the 2, ++a: After the use of self-added  9, binary conversion octal: 0 For example:072 16 binary: 0x do the Mark:0x23 summary 1: All types of data can be defined with VAR typeof is used to detect a variable of type Boolean value only two values undefined type has only one value, undefined, is mainly used to distinguish whether a variable is undefined or undefined after it is not assigned, the conversion to a value is a representation of nan nUll: A pointer to an empty object, except that the object temporarily does not exist, and the conversion to a numeric value is 0 Summary 2: "",0, null,undefined, nan, false is automatically converted to false. The others will be converted to true: empty arrays, objects, function definitions are automatically converted to true. *,/,-are used only for numeric operations, and when these operators are used with strings, the strings are cast to numbers.
JavaScript First Knowledge
