How can i search and replace strings in Node JS

Question

I am trying to write some code which allows me to pass a doc as a string which is either plain txt or html and has some fields embeded i want to replace with personal values. something like for example like this

Hi {{ first_name | fallback: "there" }},

i will pass the field names as an object with same name so the lookup is easy. So what i am looking for coding ideas how to search for the {{ }} part and then check if field is not unknown, null or "" and if it is apply the fallback value in the tag. This is something like mailmerge but i dont want ths to be a docx file and output as word or pdf. i just want the processed string so i can pass back to my mail code and send message

Answer 1

Program that will do the following to achieve your output,

1. Get the string enclosed between {{}}
2. Split the sting by |
3. Remove unwanted space using trim()
4. Check and find the fallback value
5. Replace the sting with desired value

Here is the example program that will do the above operation on step by step.

var str = 'Hi {{ first_name | fallback: "there" }},'
var data = {
    first_name: "siva",
    last_name: "sankar",
    code: 29
}

function templateRender(str, data) {
    return str.replace(/{{([^}]+)}}/g, function (match, string) {
        var fallback = ''
        var stringArr = string.split("|");
        var value = stringArr[0].trim();

        if (stringArr[1]) { fallback = stringArr[1].match(/(?<=fallback\:\s?)(["'].*?["'])/)[0].replace(/["']/g, "").trim(); }
        return data[value] ? data[value] : fallback;
    });
}

console.log("New String :::: ", templateRender(str, data));

Answer 2

Look at HandlebarsJs. It is exactly what Handlebars does, https://handlebarsjs.com

For your fallback you can use if.

{{#if first_name}}{{first_name}}{{else}}there{{/if}},

Which will default to there if first_name is falsey.

If you think if is a bit verbose you can write a helper function for defaults.

Handlebars.registerHelper('fallback', (val, def) => val || def);

and use it in a template

Hi {{fallback first_name 'there'}},

 const template = Handlebars.compile(`Hi {{#if first_name}}{{first_name}}{{ else }}there{{/if}},`); console.log(template({ first_name: '' })); console.log(template({ first_name: 'Billy' })); Handlebars.registerHelper('fallback', (val, def) => val || def); const templateWithFallback = Handlebars.compile(`Hi {{fallback first_name 'there'}},`); console.log(templateWithFallback({ first_name: '' })); console.log(templateWithFallback({ first_name: 'Billy' }));

 <script src="https://cdnjs.cloudflare.com/ajax/libs/handlebars.js/4.1.0/handlebars.min.js"></script>