JavaScript / ESLint Rules in SAPUI5

Question

I want to transform this method, to fully apply to ESLint rules in SAP WEB IDE:

getBase64Promise: function (file) {
        return new Promise((resolve, reject) => {    // <-- 
            const reader = new FileReader();
            reader.readAsDataURL(file);
            reader.onload = () => {                  // <--
                let encoded = reader.result.replace("data:", "").replace(/^.*;base64,/, "");  // <--
                if ((encoded.length % 4) > 0) {
                    encoded += '='.repeat(4 - (encoded.length % 4));
                }
                resolve(encoded);
            };
            reader.onerror = error => reject(error); // <--
        });
},

ESLint fails with these rules:

• parenthesized pattern using "=>" should be replaced
• also "let" should be replaced

Could anyone help? I tried some things but it does not work at all:

getBase64Promise: function (file) { 
  return new Promise(function (resolve, reject) {
        var reader = new FileReader();
        reader.readAsDataURL(file);
        reader.onload(function () {
            var encoded = reader.result.replace("data:", "").replace(/^.*;base64,/, "");
            if ((encoded.length % 4) > 0) {
                encoded += "=".repeat(4 - (encoded.length % 4));
            }
            resolve(encoded);
        });

        reader.onerror(function () {
            reject(reader.error);
        });
  });
},

Thanks Chris

Answer 1

The => or arrow function is a short cut to create an anonymous function. It's also a way of binding the current scope to a function without having to explicitly add .bind(this).

You can replace it fairly easily by changing this:

(params) => {

to

function(params) {

So something like

getBase64Promise: function(file) { 
  return new Promise(function(resolve, reject) {
        var reader = new FileReader();
        reader.readAsDataURL(file);
        reader.onload(function() {
            var encoded = reader.result.replace("data:", "").replace(/^.*;base64,/, "");
            if ((encoded.length % 4) > 0) {
                encoded += "=".repeat(4 - (encoded.length % 4));
            }
            resolve(encoded);
        });

        reader.onerror(function() {
            reject(reader.error);
        });
  });