Something in [] inside the function means dispensable.
Function
Custom functions
function declaration:
function name ([argument list]) {
function body;
[Return value];
}
(both the argument list and the return value are optional)
Call to function:
Call directly: function name ()
Event Invocation:
1, <input type= "button" value= "+" onclick= "f ()"/>
2, <p id= "a" ></p>
document.getElementById ("a"). Onclick=f;
function f () {
}
3, document.getElementById ("a"). Onclick=function () {} anonymous function
Parameters for the function:
Formal arguments (parameters): Defining the variables in parentheses when a function declaration
Actual arguments (arguments): Defining the variables in parentheses when a function is called
Formal parameters and argument passing:
Pass the actual argument to the formal parameter, the process of assigning a value to the formal parameters
eval (); parsing function
function return value
Return End Function and let the function have a value, in a function can have multiple return, but only the first return has effect
Return function value is undefined
return "Sadas"; function value is "Sadas"
return a+b; function value is the result of an expression
return true/false; function value is True/false
Processing of function return values:
can be used as actual parameters
can also be used as a value of a variable
can be directly output
Can be used in another function
Scope of variable:
Global variables: Variables declared in the function body with VAR or var declaration in the function body are called global variables
Scope of global variables: is the current document
Life cycle of global variables: destroy after browser shutdown
Local variables: Variables declared in the function body with VAR are local variables
Scope of local variable: is the current function
The life cycle of a local variable: The current function is destroyed when it is finished.
Overload of function: There is no overload in the JS language (function is called method)
Overload:
The method name (function name) is the same, the argument list is different or the number of parameters is different or the data type of the parameter is different
function f (a,b) {
return a+b;
}
function f (a,b,c) {
return a+b+c;
}
In other functions
F (10,20)
F (10,20,309)
F (10,20,213)
Call a different function based on the number of subsequent arguments
And in JS inside
Regardless of the number of arguments behind it is the latter function that is called by several
