Reference assignment and value assignment of JS

Last Update:2016-07-28 Source: Internet

Author: User

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To say the method of assigning JS to the first to explain the value of JS type: basic type and reference Type.1. Basic TypeThe basic data Types Are: Undefined,boolean,number,string,null. The base type is stored in the stack, and access is accessed by value, which means that you can manipulate the actual values stored in the Variable.When the basic type of data is assigned a value, the actual value is assigned, A and B are not associated, B is copied from a and is independent of each other. (the literal is the basic Type)var a=10;var b=a;Console.log (a + ', ' +b); 10,10 a++; Console.log (a + ', ' +b)//11,10 2. Reference typeA reference type refers to an object. You can have properties and methods, and we can modify their properties and METHODS. The reference object is stored in the stack by storing the object variable name and the address of the object in the heap, and storing the data in the HEAP.The object uses a reference Assignment. When we assign an object to a new variable, the assignment is actually the address of the object in the heap, not the data in the HEAP. That is, two objects point to the same storage space, regardless of which object changes, is actually changing the contents of the storage space, therefore, two objects are Linkage.3. Array is a reference typeLet's first look at an example:var a = [1,2,3]; var b = a a = [4,5,6 Alert(b); //[1,2,3] It seems that the array is the same as the base type: But:var a = [1,2,3]; var b = a; a pop () Alert(b); //[1,2] What's going on? Because: (knowing the Explanation)A = [4,5,6];//changes a reference itself, does not change the array object, A and B are not related. A.pop ();//change is an array object, a reference does not change. b = A;//the operation, B points directly to the array object, not B to a,a and then to the Array. //so Changing a reference does not affect the B reference, changing the array Object Can. Intopass links: https://www.zhihu.com/question/26042362/answer/31903017 source: know the question is the same as the one I mentioned earlier in the React todo-list article:var tasks=this.state.data; Tasks=tasks.filter (function (i) { Return i.index!=taskid; });Since the filter function returns a new array, although it is still being received with tasks, the tasks point is already a new array, so tasks and data are no longer related. (concat also returns a new Array)While the push and splice functions operate on the original array, the so-called operation in the original array refers to the invariant, so tasks and data are Associated.4. Parameter PassingThe function parameter of JS is passed as a value pass.When you pass in a primitive type parameter: it's just a copy of the content to i, and I has no relationship with Age.function Setage (i){Alert (i);//24I =;Alert (i); The change of//18,i will not affect the age outside}; var age =;setage (age);Alert (age);//24When an incoming parameter is a reference type:function SetName (obj){obj.name = ' haha ';}; var obj2 = new Object ();setName (obj2);Alert (obj2.name); Haha this looks much like passing is a reference, because the obj.name is changed, but in fact is not, actually is the value, because the value of OBJ2 itself is the address of the new object , so the address is passed IN. This is Ali's 2014 written question: var a = 1;var obj = {B:2};var fn = function () {};fn.c = 3; function Test (x, y, z) {x = 4;y.b = 5;z.c = 6;return z;}test (a, obj, fn);Alert (a + obj.b + fn.c);Answer: 12First the test passed in the argument, A is the basic type (ah yes, copied a value of wow), obj is an object (point to address hula啦, you move me also move), FN is certainly not the basic type. When the test is executed, x is assigned a value of 4 (with a ok, each play, A is still 1), Y's B is assigned to 5, then the B of obj becomes 5,z C becomes 6, then the FN C of course will be 6. So the result of alert should be 1+5+6 =12. (in fact, test does not return Z as well, Z still changes).————————————Reference: http://www.2cto.com/kf/201401/273413.html, 1190000002789651#articleheader0Reference assignment and value assignment of JS

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Reference assignment and value assignment of JS

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