Using '+' as an actual + operator when passed as string - React

Question

I am setting a state property as such: state = { sign: '' } and set it to either '+' or '-'.

The plan is to then use this within a calculation. For example, imagine sign is set to '+', I will use the operator in a calculation such as: 12 sign 8. However, when I am outputting the result, I am getting 12+8 rather than 20.

Any thoughts on where I am going wrong?

`const operator = sign === '-' ? -1 : 1; 12 + (operator) * 8`. — dfsq, Jan 11 '18 at 10:14
Also note that in mathematics sign '+' '-' has different meaning than the binary operators '+' and '-', so you better call your property operator. That is state= {operator: ''} — croraf, Jan 11 '18 at 10:14

score 2 · Accepted Answer · answered Jan 11 '18 at 10:15

Using conditionals
Using switch

var sign = '+';
console.log("Using conditionals");
console.log(sign==='+' ? 12+8 : 12-8);

//Switch
console.log("Using switch");
switch(sign)
{
    case '+' : console.log(12+8);break;
    case '-' : console.log(12-8);break;
    default : console.log("not valid operation");
}

score 1 · Answer 2 · answered Jan 11 '18 at 10:14

1

Make use of eval function

eval(a + this.state.sign + b)

The argument of the eval() function is a string. If the string represents an expression, eval() evaluates the expression

answered Jan 11 '18 at 10:14

Shubham Khatri

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score 0 · Answer 3 · edited Jan 11 '18 at 12:01

0

there is eval() in javascript to evaluate a string.

var operation=12+ sign+ 8
console.log(eval(operation))

edited Jan 11 '18 at 12:01

empiric

7,825
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answered Jan 11 '18 at 10:18

Negi Rox

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score 0 · Answer 4 · answered Jan 11 '18 at 10:19

0

Use eval in javascript

Reference

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval

 state = { sign: '+' }

console.log(eval(2 + this.state.sign + 6))

answered Jan 11 '18 at 10:19

Nisal Edu

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Using '+' as an actual + operator when passed as string - React

4 Answers4