How to decode the JWT encoded token payload on client-side in angular 5?

Question

I am getting one JWT encoded access token from my API in response. But I am not able to decode it and get it in JSON format. I tried using the angular2-jwt library for it, b

Answer 1

I have defined my JWTService as below! Hope it helps. It is in TypeScript but can be used in vanilla javascript by just copying the code.

import { Injectable } from "@angular/core";

@Injectable()
export class JWTService {
    private chars: string = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
    private atob(input) {
        var str = String(input).replace(/=+$/, '');
        if (str.length % 4 == 1) {
            throw new Error("'atob' failed: The string to be decoded is not correctly encoded.");
        }
        for (
            // initialize result and counters
            var bc = 0, bs, buffer, idx = 0, output = '';
            // get next character
            buffer = str.charAt(idx++);
            // character found in table? initialize bit storage and add its ascii value;
            ~buffer && (bs = bc % 4 ? bs * 64 + buffer : buffer,
                // and if not first of each 4 characters,
                // convert the first 8 bits to one ascii character
                bc++ % 4) ? output += String.fromCharCode(255 & bs >> (-2 * bc & 6)) : 0
        ) {
            // try to find character in table (0-63, not found => -1)
            buffer = this.chars.indexOf(buffer);
        }
        return output;
    };

    parseJwt(token) {
        var base64Url = token.split('.')[1];
        var base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
        var jsonPayload = decodeURIComponent(this.atob(base64).split('').map(function (c) {
            return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
        }).join(''));

        return JSON.parse(jsonPayload);
    };
}