Peek Operation in Stack Using Javascript
How Can I Get the First Element from My Stack Here Is My Code Var Stack = []; Stack. Push(Id1); Stack. Push(Id2); I Know There Is Something Like Peek in Java...
How can I get the first element from my stack here is my code
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?
6 Answers
To check the topmost element unfortunately you must explicitly index it
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 slice call.
// The same as stack[stack.length-1], just slower and NOT idiomatic
var top = stack.slice(-1)[0];
To extract an element there is however pop:
// Add two top-most elements of the stack
var a = stack.pop();
var b = stack.pop();
stack.push(a + b);
var stack = [];
stack.push("id1");
stack.push("id2");
console.log(stack[stack.length-1]); // the top element
console.log(stack.length); //sizeEdited 2022:
Now you can just use stack.at(-1)
If you just need one edge of your stack (head or tail is not matter) use it reversed:
I mean :
peek() become array[0],
unshift(v) become push()
shift() become pop()
some code:
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
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());I just want to add here the .at prototype function. Documentation is found here:
So, to get the peek is as simple as:
[array].at(-1);
Example:
const stack = [];
stack.push("sample1");
stack.push("sample2");
console.log(stack.at(-1)) // sample2
var stackArr = [1,2,3,4];
console.log(stackArr[stackArr.length-1]);
//expected output is 4; var stack = [];
stack.push("id1");
stack.push("id2");
var topObj = stack[0]
console.log(topObj)
David Miller brings 15 years of experience in global economics, personal finance strategy, and market dynamics. He specializes in turning complex economic trends into actionable insights for everyday readers.
