JavaScript variable being ignored

问题

So I'm trying to write a Data Structures Visualizer with JS (so that I can host it online). It seems as though my JS ignoring my variables (and claiming some functions don't exist) and I can't figure out why. I'd appreciate the help.

var stack = new Stack();
var defaultValueCounter = 0;
function push() {
    var value = document.getElementById("add").value;
    if (value === "") {
        defaultValueCounter++;
        value = defaultValueCounter;
    }
    //console.log(stack + ", " + value)
    stack.push(value);
    addCol(value);
    stack.print();
    document.getElementById("add").value = "";
}

In that code, it seems to ignore stack for some reason (initializes to undefined). I've tested this hypothesis by moving the declaration inside the push() function, and it works (although for obvious reasons, my Stack can only contain 1 element). What can I do to fix it

Edit: Sharing my Stack implementation

function Node() {
    this.value;
    this.next ;
}

var Stack= function(){
    this.head;
}

Node.prototype.insert=function(value) {
    var current = this;
    if (current.value === undefined) { //has nothing yet
        current.value = value; //insert here
        return;
    }

    if(current.next === undefined) { //completely null
        current.next = new Node();//want new node
    }
    var c = current.next;
    c.insert(value);
}

Stack.prototype.push= function(value) {
    if(value==undefined || value==""){
        throw "Please input proper value (number)"
    }
    if(this.head==undefined){//nothing exists yet
        this.head=new Node();
        this.head.value=value;
    }else{//nonempty stack
        var c=this.head;
        c.next=new Node();
        c.next=this.head;
        c.value=value;
        this.head=c;
    }   
}


Stack.prototype.top= function() {   
    if(this.head==undefined){//nothing exists yet
        throw "Trying to get top of null"
    }else{//nonempty stack
        return this.head.value;
    }   
}

Stack.prototype.pop= function() {

    if(this.head==undefined){//nothing exists yet
        throw "Trying to get top of null"
    }else{//nonempty stack
        var val=this.head.value;
        this.head=this.head.next;
        return val;
    }   
}

Stack.prototype.print= function(){
    //debugging purposes
    var c=new Node();
    c.value=this.head.value
    c.next=this.head.next
    while(c.value!=undefined){
        console.log(c.value)
        c=c.next
    }
    console.log("Head: "+ this.value)
}

Edit: It seems as though the code is not initializing the stack at the beginning. What can I do to resolve this?

回答1:

For some reason, I resolved all issues by deleting top(). Not sure why. Will investigate my code futher

回答2:

You perhaps need to use

function Stack() {

instead of

var Stack = function() {

as function definitions are hoisted, where as only var declarations, not var definitions are hoisted

This explains why Stack is undefined

Also, your nonempty stack code should be

}else{//nonempty stack
    var c=new Node;
    c.next = this.head;
    c.value=value;
    this.head=c;
}   

回答3:

You have a problem with scope. stack is declared outside of the function and not passed to the function. Hence, it is undefined when you try to access it.

To fix this, ensure that the method push() operates on the stack variable by making variable visible to the function.

来源：https://stackoverflow.com/questions/61857251/javascript-variable-being-ignored