为什么在节点更改时将原型中的var node = this.obj辅助而不是this.obj？
[英]Why does assiging var node= this.obj inside a protoype not this.obj when node changes?
问题描述
I'm implementing a simple linked list in javascript using prototypes. 
我正在使用原型在javascript中实现一个简单的链接列表。 I came across something I don't quite understand - 我遇到了我不太了解的事情-
var Node = function( value ) {
this.value = value;
this.next = null;
};
var List = function( head ) {
this.head = null;
};
List.prototype.insert = function( value ) {
if ( this.head === null ) {
this.head = new Node( value );
} else {
var aNode = this.head;
console.log( 'same: ' + (aNode === this.head)); // prints true
while ( aNode.next !== null ) {
aNode = aNode.next;
}
var node = new Node( value );
aNode.next = node;
console.log( 'Head: ' + this.head.value ); //prints 1
console.log( 'Node: ' + aNode.value ); //prints 2,3,4
}
};
var aList = new List();
aList.insert( 1 );
aList.insert( 2 );
aList.insert( 3 );
aList.insert( 4 );
If this.head and aNode share a reference, changing aNode to aNode.next doesnt change this.head. 如果this.head和aNode共享引用，则将aNode更改为aNode.next不会更改this.head。 Can someone explain why? 有人可以解释为什么吗？ I'm new to prototypes. 我是原型的新手。
3 个解决方案
解决方案1
2 2015-08-04 16:40:14
Because of the order of operations. 由于操作顺序。 You want parentheses on that: 您想要在其上加上括号：
console.log( 'same: ' + (aNode === this.head))
// ---------------------^-------------------^
Without them, it's effectively 没有他们，这是有效的
console.log( ('same: ' + aNode) === this.head)
...(which is, of course, false) because + has a higher precedence than === . ...（这当然是假的），因为+的优先级高于=== 。 It's the same reason that if (a + 5 === 6) is true when a is 1 . 同样的原因是当a为1时if (a + 5 === 6)为true。
解决方案2
0 2015-08-04 16:45:08
In your console.log it is first evaluating the concatenation of same string and aNode and then comparing to this.head : 在console.log它首先评估same字符串和aNode的串联，然后与this.head进行比较：
Change it to: 更改为：
console.log( 'same:' + (aNode === this.head))
or: 要么：
console.log( 'same:', aNode === this.head)
解决方案3
0 2015-08-04 17:39:55
This should do the trick... let me know. 这应该可以解决问题...让我知道。
- Declare a new list, example ---
var chores = new List("chores");声明一个新列表，例如--- var chores = new List("chores"); - Declare a new list item, example ---
chores.add("Mow lawns.");声明一个新的列表项，例如--- chores.add("Mow lawns.");
//CODE //码
<!DOCTYPE html>
<html>
<head>
<script>
//LIST (OBJECT CONSTRUCTOR)
var List = function(title){
this.title = title;
this.datetime = new Date();
this.items = [];
};
//LIST (OBJECT METHOD - ADD)
//ALL OBJECTS CREATED FROM THE LIST OBJECT CONSTRUCTOR ABOVE INHERIT THIS METHOD
List.prototype.add = function(val){
this.items.push(val);
};
//CREATE NEW LIST OBJECT CALLED (CHORES)
var chores = new List("chores");
//INPUT DATA USING LIST METHOD ADD, WHICH OBJECT CHORES INHERITED WHEN IT WAS INSTANTIATED (CREATED)
chores.add("Mow lawns.");
chores.add("Make dinner.");
chores.add("Drive to the store.");
//VIEW OUTPUT
console.log(chores);
console.log(chores.items);
console.log(chores.items[0]);
console.log(chores.items[1]);
console.log(chores.items[2]);
</script>
</head>
<body>
</body>
</html>
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