JS - "addition operator" and "subtraction operator" to number

Question

It is necessary to rewrite all the values of the array into a new variable, but so that the addition operator and subtraction operator is not be like a string, that is, so that the code is executed and the result is 3

How can my problem solve?

Code:

<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<script>
let a = "1 + 3 - 1";
let arr = a.split(" ");

arr.forEach(function(item, i, arr) {});

//code here


</script>
</body>
</html>

There is no simple way of doing it.... eval and new Fuction() are one way. Or plenty of libraries out there to solve math. — epascarello, May 18 '21 at 12:27
You could [write your own simple expression parser](https://stackoverflow.com/a/64934466/) (scroll to the bottom for an example that supports addition). Althought you can probably just use an existing AST parser and work on that output to evaluate it. Or use a library to do it for you. Not sure *why* you want to evaluate strings and how you want to do this. — VLAZ, May 18 '21 at 13:08

Mamun · Accepted Answer · 2021-05-18T12:33:33.637

1

You do not need any array or loop here, you can use eval():

<!DOCTYPE html>
<html>
  <head>
    <title>Page Title</title>
  </head>
  <body>
    <script>
      let a = "1 + 3 - 1";
      let res = eval(a);
      console.log(res);
    </script>
  </body>
</html>

edited May 18 '21 at 12:33

answered May 18 '21 at 12:27

Mamun

66,969
9
47
59

While you can use `eval()`, it is a huge security risk and should really be avoided for a problem as simple as this. – samanime May 18 '21 at 12:47
I read about security risk. If no eval(), how else this code can be solved? – Deni Wassulmaier May 18 '21 at 13:00

Praveen M · Answer 2 · 2021-05-22T18:26:51.863

0

use if condition(for example: if(i == "+"){}) to sort out accordingly with the next number. This is My Idea.I am Beginner in Js. Please debug this Script For Example:

<script>
arr = ["5" , "+" , "1" , "-", "1"];
k=arr.length;
z=[];
evolve();
function evolve(){
 for(i=0; i < k ; i = i+2) {
    for(j=0;j>-1;j++){
         if(arr[i] == `${j}`){
                z.push(j);
                evovle();
}
}
}
}
y=z[0]
ind =1
for(i=1;i<k;i = i+2){
     if(arr[i] == "+"){
      y=y+z[ind];
     ind++
      }
     if(arr[i] == "-"){
      y=y-z[ind];
     ind++
      }
}
</script>
<h1>{{y}}</h1>

edited May 22 '21 at 18:26

answered May 18 '21 at 12:34

Praveen M

11
3

Problem in addition operator. How it can change from string to addition operator – Deni Wassulmaier May 18 '21 at 13:02
The answer is saying you do the math.... You detect the operator and you add the numbers in the array that are to the left and right of it – epascarello May 18 '21 at 13:03
Please check my recent edit and check any other mistake in there. Thankyou – Praveen M May 20 '21 at 05:17

JS - "addition operator" and "subtraction operator" to number

2 Answers2