How to convert an expression from string to number (JS) [duplicate]

There are two options. The first option is eval() , the second is mathematics. The first option is not the best in terms of security, but convenient (for the developer).

Here is an example of how to solve this problem with the help of mathematics:

 var z = 0; var operat = [1, -1]; var rand1 = operat[Math.floor(Math.random() * operat.length)]; var rand2 = operat[Math.floor(Math.random() * operat.length)]; var reZ1 = Math.floor(Math.random() * (10 - 1 + 1)) + 1; var reZ2 = Math.floor(Math.random() * (10 - 1 + 1)) + 1; console.log(reZ1, reZ2); z = z + rand1 * reZ1 + rand2 * reZ2; console.log(z); 

OR

 function rand(min, max){ return Math.floor(Math.random() * (max-min + 1)) + min; } var z = 0, rand1 = Math.random()<0.5?-1:1; rand2 = Math.random()<0.5?-1:1; reZ1 = rand(10,1)*rand1, reZ2 = rand(10,1)*rand2; console.log(reZ1, reZ2); z = z + reZ1 + reZ2; console.log(z); 

can use Eval()

 var z = 0; var operat = ['+', '-']; var rand1 = operat[Math.floor(Math.random() * operat.length)]; var rand2 = operat[Math.floor(Math.random() * operat.length)]; var reZ1 = Math.floor(Math.random() * (10 - 1 + 1)) + 1; var reZ2 = Math.floor(Math.random() * (10 - 1 + 1)) + 1; console.log("z =", z + rand1 + reZ1 + rand2 + reZ2); z += eval(rand1 + reZ1 + rand2 + reZ2); console.log(z); 

but in order to cut off the "pampering" of users at the input of Eval() it is better to actually submit the result of a regular expression, in your case these are the numbers \d and +-
as an example, the code left, it works
but for more close to life tasks, it is recommended to replace the line with:
z += eval((rand1 + reZ1 + rand2 + reZ2).match(/^[\d+-]*/g));
or faster alternatives