For the question of whether the JavaScript function parameter is a byVal or a pass (BYREF), there is a common misconception that "simple types" such as number,string are values, number, String, Object, array, and so on "complex types." is the address.
Isn't that right? Why is there such a misunderstanding? Take a look at these two pieces of code:
Copy Code code as follows:
Code that creates the illusion of passing values
function Modifylikebyval (x) {
x = 1;
Console.log (' x =%d ', x);
}
var x = 0;
Console.log (' x =%d ', x); Output x = 0
Modifylikebyval (x); Output x = 1
Console.log (' x =%d ', x); Output x = 0 x not changed!
Copy Code code as follows:
Code that creates a false message
function Modifylikebyref (x) {
X[0] = 4;
X[1] = 5;
X[2] = 6;
Console.log (' x = [%s] ', X.join (', '));
}
var x = [1, 2, 3];
Console.log (' x = [%s] ', X.join (', ')); Output x = [1, 2, 3]
Modifylikebyref (x); Output x = [4, 5, 6]
Console.log (' x = [%s] ', X.join (', ')); Output x = [4, 5, 6] x has changed!
As a result, the above code concludes that "simple Type" as a parameter is a value (ByVal), and that "complex type" is a pass (byRef) argument.
What's the problem?
With a careful look at two functions, you can find a point:
In ByVal, The parameter x:x = 1 is directly modified;
In ByRef, the member that modifies the parameter x: x[0] = 4; X[1] = 5; X[2] = 6;
From this I guess: in JavaScript, all variables or members, are a pointer, when modifying a variable or member value, it is actually modified the address of the pointer.
So the code above can be explained:
In "ByVal":
Copy Code code as follows:
Global {//Represents a globals scope, the following representation function scope
var x = 0; Initialize pointer x and point to number 0
Fun (x) {
x = global.x; Incoming parameter global.x; The X-pointer address of the fun field points to the number 0 as the X pointer address of the global field
x = 1; Modifies the X-pointer address of the fun field, pointing to the number 1;
The//Fun field ends, the x pointer in the global field does not change
}
In "ByRef":
Copy Code code as follows:
Global {//Represents a globals scope, the following representation function scope
/*
Initializes the pointer x and points to the array [1, 2, 3]
is actually X's three members 0, 1, 2, respectively pointing to 1, 2, 3;
*/
var x = [1, 2, 3];
Fun (x) {
x = global.x; Incoming parameter global.x; The X-pointer address of the fun field points to the array as the X pointer address of the global field [1, 2, 3]
/*
X in the Fun field is not changed again
Then modify the pointer of the x (i.e. global.x) three member pointers in the fun field
*/
X[0] = 4;
X[1] = 5;
X[2] = 6;
The//fun domain ended, the x pointer in the global field did not change, but its three member pointers were changed, so we saw the results of our output
}
So how does this code explain???
Copy Code code as follows:
(function (A, b) {
Arguments[0] = 1;
b = 2;
Console.log (arguments, a, b);
}) (-1,-2);
Can only say A, b ..., is arguments[0],... [N] alias.
If there is something wrong, please point it out, thank you.
If there is a better explanation, you are welcome to share.
