I'm trying to make a Javascript function that will take a mathematical expression and apply it to a predefined number, for example:
var myNum = 10;
function EQ(eq){
// code here
}
For example the input should me something like this:
EQ("*100/10"); //output 100
EQ("+100"); //output will be 110
EQ("-+=1"); //output false
Is there any way to do that? Thanks
You could probably work eval() into a simple solution. For instance:
var myNum = 10;
function EQ(eq) { return eval(myNum+eq); }
alert( EQ("*100/10") ); // outputs 100
I'd encourage you to expand upon this by implementing a try-catch and handling exceptions.
EQ(). In the data you provided, and in my solution, it is assumed the first char will always (without variance) be an operator. If you pass in 100/10 then the evaluated expression will be 10100/10, which is 1010.Try...Catch in Javascript: w3schools.com/js/js_try_catch.aspHere's a simple expression evaluator:
function evalExpression(text)
{
var tokens = text.split(" ");
var output = [];
var operators = [];
var reNumber = /^\d+(\.\d+)?$/;
var reOperator = /^[\/\+\*\-]$/;
var precedence = { "+": 1, "-": 1, "*": 2, "/": 2 };
for (var i = 0; i < tokens.length; ++i)
{
var t = tokens[i];
if (reNumber.test(t))
output.push(Number(t));
else if (reOperator.test(t))
{
while (operators.length && precedence[t] <= precedence[operators[operators.length - 1]])
{
output.push(operators.pop());
}
operators.push(t);
}
else if (t == "(")
operators.push(t);
else if (t == ")")
{
while (operators.length && operators[operators.length - 1] != "(")
output.push(operators.pop());
if (!operators.length) return false;
operators.pop();
}
else
return false;
}
while (operators.length)
output.push(operators.pop());
var result = [];
for (i = 0; i < output.length; ++i)
{
t = output[i];
if (reNumber.test(t))
result.push(t);
else if (t == "(" || result.length < 2)
return false;
else
{
var lhs = result.pop();
var rhs = result.pop();
if (t == "+") result.push(lhs + rhs);
if (t == "-") result.push(lhs - rhs);
if (t == "*") result.push(lhs * rhs);
if (t == "/") result.push(lhs / rhs);
}
}
return result.pop();
}
It supports numbers and + - * / ( ). Tokens must be separated by a single space, e.g.: "1 * ( 2 + 3 )"
Anyway, that's the type of code you'd need if you didn't want to use eval.
try this...
function EQ(input) {
try {
var ret = Number(eval('(0+(' + input + '))'));
return isNaN(ret) ? null : ret;
} catch(err) {
}
return null;
}You can replace the null default with a literal false if you like...
