如何使用JavaScript在其他特定字符之前插入字符

Question

I need to know how to insert an asterix before an open bracket.

I am doing multiplication using javascript's eval , for example, eval("2(3)") , but I am getting the error "unexpected input value" .

To solve this I need the following:

var str = "2(3)";

to be changed to this:

output = "2*(3)";

Answer 1

You can use String.prototype.replace() .

Example:

 var str = '2(3)' var output = str.replace(/\\(/g, '*(') console.log(output) 

That will output: 2*(3)

Answer 2

If you want to perform more complex/nested multiplication you need to use this more complicated regex (\\)|\\d+(?!\\d)\\.?)(?=[(\\d.+-]) with the replace() function. It will work for any combination of nested brackets, as well as plus signs, negative numbers and numbers starting or ending with a decimal point:

 var str, output; str = '2(3)'; output = str.replace(/(\\)|\\d+(?!\\d)\\.?)(?=[(\\d.+-])/g, '$1*'); console.log(output); str = '2(3)(-4)'; output = str.replace(/(\\)|\\d+(?!\\d)\\.?)(?=[(\\d.+-])/g, '$1*'); console.log(output); str = '((.22(33))((-44)-55.(66)+77))'; output = str.replace(/(\\)|\\d+(?!\\d)\\.?)(?=[(\\d.+-])/g, '$1*'); console.log(output); 

Answer 3

You can use the replace() function combined with a little regex ([0-9])\\(([0-9]) :

 var str = "2(3)"; var output = str.replace(/([0-9])\\(([0-9])/g,'$1*($2'); console.log(output); 

Answer 4

You can slice the string and add the asterisk sign like this:

 var str = "2(3)"; var new_str = str.slice(0, str.indexOf("(")) + "*" + str.slice(str.indexOf("(")); console.log(new_str) 

Answer 5

Try this:

 var str = "2(3)"; var a = str.split(''); a.splice(1,0,"*"); a = a.join(''); console.log(a); 

Works good for me :)