Transfer and reference of function parameters in Javascript

Conclusion: Numbers and strings are transmitted to function parameters. Changes in function parameters do not affect external variables.

For arrays and objects, the value of the variable of the object (array) is passed to the function parameter. This variable is saved to the address of the object (array. When the function changes the content of the object (array) pointed to by this address, it also changes the content of the object (array) pointed to by the function external variable; when a function changes the address of a variable, it actually loses contact with the variable outside the function and becomes a completely different object without changing the external function object.

 

Many people think that parameters in javascript can be transmitted by values such as numbers and strings, and arrays and objects by address (reference. It is actually a type of value transfer. The example below demonstrates this point.

VaR V1 = []
VaR V2 = {};
VaR V3 = {};
Function Foo (V1, V2, V3)
{
V1 = [1];
V2 = [2];
V3 = {A: 3}
}

Foo (V1, V2, V3 );
Alert (V1); // Blank
Alert (V2); // [object]
Alert (v3.a); // undefined

It can be seen that V1, V2, and V3 are not changed, V1 is still an array of zero elements, and V2 and V3 are still blank objects.

However, passing by values such as arrays and objects refers to the value of the variable address.

The passing of values of arrays and objects is different from that of numbers and strings. Numbers and strings directly copy the values, while arrays and objects copy the variable addresses.

After we set V1, V2, and V3 as parameters to the function, we have an address copy. These address copies point to the same address as the V1, V2, and V3 addresses. However, we assigned values for V1, V2, and V3, that is, we changed the point of the address copy and pointed to the new array and object. In this way, internal V1, V2, V3, and external V1, V2, and V3 are completely disconnected.

If we operate directly without adding a new value, it still operates on the same array or object as V1, V2, and V3.

VaR V1 = []
VaR V2 = {};
VaR V3 = {A: 0 };
Function Foo (V1, V2, V3)
{
V1.push (1 );
V2.a = 2;
V3.a = 3;
}

Foo (V1, V2, V3 );
Alert (V1); // 1
Alert (v2.a); // 2
Alert (v3.a); // 3