Replacing parts of a String using RegEx - Javascript

Question

I am trying to replace the 'parameters' in my string with the actual values of the parameters using the replace() method, but for some reason I cannot get it it to work. The string I am using is:

var temp = "This {{application}} will be down from {{start}} to {{finish}}."

I want to replace {{application}} with the application name, and so on.

var regEx = /{{(.*?)}}/;

This is the regex I use to grab the values between the brackets and that part works. Here is the rest of my code:

if (regEx.exec(temp)[1] === "application") {
     temp.replace(regEx, params.value);
}

'params.value' is the name of the application. I thought this would work, but it is not.

Answer 1

To replace only a single string(static)

var appName = "application"; // String to replace
var regex = new RegExp("{{" + appName + "}}", "g"); // Use `g` flag to replace all occurrences of `{{application}}`
temp = temp.replace(regex, param.value);

 var appName = "application", regex = new RegExp("{{" + appName + "}}", "g"), temp = "This {{application}} will be down from {{start}} to {{finish}}."; var param = { value: 'StackOverflow' }; temp = temp.replace(regex, param.value); console.log(temp); document.body.innerHTML = temp; 

---

To replace all the strings inside brackets by their respective values(Dynamic)

You can use String#replace with an object to replace values.

var regex = /{{(.*?)}}/g;
// Match all the strings in the `{{` and `}}`
// And put the value without brackets in captured group

temp = temp.replace(regex, function(m, firstGroup) {
    // m: Complete string i.e. `{{foobar}}`
    // firstGroup: The string inside the brackets

    return params[firstGroup] || 'Value not found in params';
    // If the value for the key exists in the `params` object
    //     replace the string by that value
    // else
    //     replace by some default string
});

 var params = { application: 'Stack Overflow', start: 'On Sunrise', finish: 'In Dreams' }; var temp = "This {{application}} will be down from {{start}} to {{finish}}."; var regex = /{{(.*?)}}/g; temp = temp.replace(regex, function(m, firstGroup) { return params[firstGroup] || 'Value not found in params'; }); console.log(temp); document.body.innerHTML = temp; 

Answer 2

Here is an helper function to produce what you expect

function replace(str, dict) {
    return str.replace(/{{(.*?)}}/g, function(match, $1) {
        return dict[$1] || match;
    });
}

replace(
    "This {{application}} will be down from {{start}} to {{finish}}.",
    {
        'application': 'pigeon',
        'start': '8am',
        'finish': '9pm'
    }
);
// "This pigeon will be down from 8am to 9pm."

This will accept a mapping of values to replace and the replacement. And returns the string correctly formatted.

Answer 3

You can use a callback inside a replace to evaluate the capture group contents:

 var name = "Google"; var temp = "This {{application}} will be down from {{start}} to {{finish}}."; var res = temp.replace(/{{(.*?)}}/g, function (m, g) { return g === "application" ? name : m; }); document.body.innerHTML = res; 

Here, m is the whole matched text with braces and g is the submatch without braces.