使用 javascript 在堆栈中查看操作
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peek operation in stack using javascript
提问by JustCurious
How can I get the first element from my stack here is my code
我如何从我的堆栈中获取第一个元素，这是我的代码
var stack = [];
stack.push(id1);
stack.push(id2);
I know there is something like peek in java. Is there any similar method in JS using which i can get the topmost element?
我知道在 Java 中有类似 peek 的东西。JS 中有没有类似的方法可以使用它来获取最顶层的元素？
回答by 6502
To check the topmost element unfortunately you must explicitly index it
不幸的是，要检查最顶层的元素，您必须明确索引它
var top = stack[stack.length-1];
the syntax stack[-1](that would work in Python) doesn't work: negative indexes are valid only as parameters to slicecall.
语法stack[-1]（在 Python 中有效）不起作用：负索引仅作为要slice调用的参数有效。
// The same as stack[stack.length-1], just slower and NOT idiomatic
var top = stack.slice(-1)[0];
To extractan element there is however pop:
然而，要提取一个元素pop：
// Add two top-most elements of the stack
var a = stack.pop();
var b = stack.pop();
stack.push(a + b);
回答by Sagar V
var stack = [];
stack.push("id1");
stack.push("id2");
console.log(stack[stack.length-1]); // the top element
console.log(stack.length); //size回答by pery mimon
If you just need one edge of your stack (head or tail is not matter) use it reversed:
如果您只需要堆栈的一个边缘（头或尾无关紧要），请将其颠倒使用：
I mean :
我的意思是 ：
peek()become array[0],unshift(v)become push()shift()become pop()
peek()成为array[0]，unshift(v)成为push()shift()成为pop()
some code:
一些代码：
class Stack{
constructor(... args ){
this.store = [... args.reverse()];
}
peek(){
return this.store[0];
}
push(value){
return this.store.unshift(value);
}
pop(){
return this.store.shift();
}
}
const stack = new Stack(1,2,3);
stack.push(4);
console.log(stack.peek());
stack.pop();
console.log(stack.peek())or shorter
或更短
function Stack(...rest){
var store = [... rest.reverse() ];
return {
push:(v)=> store.unshift(v) ,
pop : _ => store.shift(),
peek: _ => store[0]
}
}
var stack = Stack(1,2,3);
console.log(stack.peek());
stack.push(4);
console.log(stack.peek());
stack.pop(), stack.pop();
console.log(stack.peek());回答by Abhilash A S
var stack = [];
stack.push("id1");
stack.push("id2");
var topObj = stack[0]
console.log(topObj)
