Identifier naming rules: the first character must start with a letter, underscore-, dollar sign, and can be followed by letters, underscore-, numbers' dollar sign
The scope of variables: global variables and local variables = "global declaration outside the function, local vice versa;
<script language="javascript">
var a; //The variable is declared outside the function and acts on the entire script code
function send()
{ a="JavaScript" var b="Language basics" //The variable is declared inside the function , Only works on the function body alert(a+b); }
</script>
Variable lifetime: 2 types of global and local variables = "global until the end of the program = "local until the end of the function;
2 Data type
Integer ()', floating point (flort), string (string), boolean (), undefined (undefined=>var=a or var=string notProperty;)
NaN is not a number, (null)
Assignment operation: For example: a+=b=> is equivalent to a=a+b; String operation: concatenate a string=" "name" + "study",
Boolean operators
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effect
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C
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Pascal
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equal
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==
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=
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not equal to
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!=
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<>
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Less than
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<
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<
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more than the
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>
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>
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Less than or equal to
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<=
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<=
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greater or equal to
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>=
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>=
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versus
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&&
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and
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or
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||
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or
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non-
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!
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not
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XOR
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^
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xor
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Ternary operator (condition)? :
The typeof operator operator returns the type of data currently contained in its operand. This is especially useful for judging whether a variable has been defined
new operator: create a new object