String interpolation on variable

Question

Say I have a variable str

var str = "123" 

Now I could do console.log(`Hello ${str}`) and it will print Hello 123

Now I have another variable strnew

var strnew = 'Hello ${str}' 

Note (based on answers/comments) - strnew is read from a file, so its always a string and cant be replaced with `

How do I console.log(...) to print Hello 123

Is it possible wihtout any kind of eval()

Answer 1

With something as simple as ${str} you can use a simple string replacement:

var template = (tpl, args) => tpl.replace(/\${(\w+)}/g, (_, v) => args[v]);    var tpl = 'Hello ${str} and ${other}';    console.log(template(tpl, {str: 'foo', other: 'bar'}));

In a general case, no, not possible without eval (short of writing your own js interpreter), because ${...} can contain arbitrary expressions.

For completeness' sake, here's the eval solution:

var template = function(tpl, args) {      var keys = Object.keys(args),          fn = new Function(...keys,             'return `' + tpl.replace(/`/g, '\\`') + '`');      return fn(...keys.map(x => args[x]));  };      function test() {      var myTpl = 'Hello ${str + "!"} and ${other.toUpperCase()}';      console.log(template(myTpl, {str: 'foo', other: 'bar'}));  }    test();

Answer 2

You can use function instead of just string.

var strnew = function(str){    return `Hello ${str}`;  }  var str = "123";  console.log(strnew(str))