Python's %s equivalent in Javascript?

Question

I'm currently learning NodeJS after working with Python for the last few years.

In Python I was able to save a string inside a JSON with dynamic parameters and set them once the string loaded, for example:

MY JSON:

j = {
"dynamicText": "Hello %s, how are you?"
}

and then use my string like that:

print(j['dynamicText'] % ("Dan"))

so Python replaces the %s with " Dan ".

I am looking for the JS equivalent but could not find one. Any ideas?

** Forgot to mention: I want to save the JSON as another config file so literals won't work here

Answer 1

There is no predefined way in JavaScript, but you could still achieve something like below. Which I have done in my existing Application.

function formatString(str, ...params) {
    for (let i = 0; i < params.length; i++) {
        var reg = new RegExp("\\{" + i + "\\}", "gm");
        str = str.replace(reg, params[i]);
    }
    return str;
}

now formatString('You have {0} cars and {1} bikes', 'two', 'three') returns 'You have two cars and three bikes'

In this way if {0} repeats in String it replaces all.

like formatString('You have {0} cars, {1} bikes and {0} jeeps', 'two', 'three') to "You have two cars, three bikes and two jeeps"

Hope this helps.

Answer 2

Use template literal. This is comparatively new and may not support ancient browsers

 var test = "Dan" var j = { "dynamicText": `Hello ${test}, how are you?` } console.log(j["dynamicText"]) 

Alternatively you can create a function and inside that function use string.replace method to to replace a word with new word

 var test = "Dan" var j = { "dynamicText": "Hello %s, how are you?" } function replace(toReplaceText, replaceWith) { let objText = j["dynamicText"].replace(toReplaceText, replaceWith); return objText; } console.log(replace('%s', test)) 

Answer 3

You can write a String.format method, using regex, and the String.replace method:

String.prototype.format = function() {
    var args = arguments;
    return this.replace(/{(\d+)}/g, (match, p1) => {
        var i = parseInt(p1);
        return typeof args[i] != 'undefined' ? args[i] : match;
    });
}

After that, running:

console.log("{0}{1}".format("John", "Doe"));

Will output: John Doe

Of course, if you don't like editing the prototype of objects you don't own (it is generally good practice), you can just create a function:

var format = function(str) {
    var args = arguments;
    return str.replace(/{(\d+)}/g, (match, p1) => {
        var i = parseInt(p1);
        return typeof args[i+1] != 'undefined' ? args[i+1] : match;
    });
}

Answer 4

For a few nice alternatives, you may want to take a look at JavaScript equivalent to printf/string.format

While it's asking for a C-like printf() equivalent for JS, the answers would also apply to your question, since Python format strings are inspired by C.

Answer 5

I've found a great npm module that does exactly what I was needed - string-format .

String-Format in NPM