Open In App

JavaScript | Encode/Decode a string to Base64

Improve
Improve
Like Article
Like
Save
Share
Report

In order to encode/decode a string in JavaScript, we are using built-in functions provided by JavaScript.

btoa() Method

This method encodes a string in base-64 and uses the “A-Z”, “a-z”, “0-9”, “+”, “/” and “=” characters to encode the provided string.

Syntax:

window.btoa( String )

Parameter (String): This parameter is required. It specifies the string to be encoded.

atob() Method

This method decodes a base-64 encoded string, which has been encoded by the btoa() method.

Syntax:

window.atob( String )

Parameter (String): This parameter is required. It specifies the string which has already been encoded by the btoa() method.

Here are few of the examples.

Example 1: This examples encodes the string “This is GeeksForGeeks” by btoa() function.

Javascript




function encodeStr() {
    console.log(btoa(str));
}
 
const str = "This is GeeksForGeeks";
encodeStr();


Output

VGhpcyBpcyBHZWVrc0ZvckdlZWtz

Example 2: This examples decodes the string “VGhpcyBpcyBHZWVrc0ZvckdlZWtz” encoded by btoa() function with the help of atob() function.

Javascript




function decodeStr() {
    console.log(atob(str));
}
 
const str = "VGhpcyBpcyBHZWVrc0ZvckdlZWtz";
decodeStr();


Output

This is GeeksForGeeks

The Cross-Browser Method is used as a JavaScript library to encode/decode a string in any browser.

Example 3: This examples encodes the string “This is GeeksForGeeks” by creating a Base64 object.

Javascript




let Base64 = {
    _keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
        "abcdefghijklmnopqrstuvwxyz0123456789+/=",
    encode: function (e) {
        let t = "";
        let n, r, i, s, o, u, a;
        let f = 0;
        e = Base64._utf8_encode(e);
        while (f < e.length) {
            n = e.charCodeAt(f++);
            r = e.charCodeAt(f++);
            i = e.charCodeAt(f++);
            s = n >> 2;
            o = (n & 3) << 4 | r >> 4;
            u = (r & 15) << 2 | i >> 6;
            a = i & 63;
            if (isNaN(r)) {
                u = a = 64
            } else if (isNaN(i)) {
                a = 64
            }
            t = t +
                this._keyStr.charAt(s) +
                this._keyStr.charAt(o) +
                this._keyStr.charAt(u) +
                this._keyStr.charAt(a)
        }
        return t
    },
    decode: function (e) {
        let t = "";
        let n, r, i;
        let s, o, u, a;
        let f = 0;
        e = e.replace(/[^A-Za-z0-9\+\/\=]/g, "");
        while (f < e.length) {
            s = this._keyStr.indexOf(e.charAt(f++));
            o = this._keyStr.indexOf(e.charAt(f++));
            u = this._keyStr.indexOf(e.charAt(f++));
            a = this._keyStr.indexOf(e.charAt(f++));
            n = s << 2 | o >> 4;
            r = (o & 15) << 4 | u >> 2;
            i = (u & 3) << 6 | a;
            t = t + String.fromCharCode(n);
            if (u != 64) {
                t = t + String.fromCharCode(r)
            }
            if (a != 64) {
                t = t + String.fromCharCode(i)
            }
        }
        t = Base64._utf8_decode(t);
        return t
    },
    _utf8_encode: function (e) {
        e = e.replace(/\r\n/g, "\n");
        let t = "";
        for (let n = 0; n < e.length; n++) {
            let r = e.charCodeAt(n);
            if (r < 128) {
                t += String.fromCharCode(r)
            } else if (r > 127 && r < 2048) {
                t +=
                    String.fromCharCode(r >> 6 | 192);
                t +=
                    String.fromCharCode(r & 63 | 128)
            } else {
                t +=
                    String.fromCharCode(r >> 12 | 224);
                t +=
                    String.fromCharCode(r >> 6 & 63 | 128);
                t +=
                    String.fromCharCode(r & 63 | 128)
            }
        }
        return t
    },
    _utf8_decode: function (e) {
        let t = "";
        let n = 0;
        let r = c1 = c2 = 0;
        while (n < e.length) {
            r = e.charCodeAt(n);
            if (r < 128) {
                t += String.fromCharCode(r);
                n++
            } else if (r > 191 && r < 224) {
                c2 = e.charCodeAt(n + 1);
                t += String.fromCharCode(
                    (r & 31) << 6 | c2 & 63);
 
                n += 2
            } else {
                c2 = e.charCodeAt(n + 1);
                c3 = e.charCodeAt(n + 2);
                t += String.fromCharCode(
                    (r & 15) << 12 | (c2 & 63)
                    << 6 | c3 & 63);
                n += 3
            }
        }
        return t
    }
}
 
function encodeStr() {
    console.log(Base64.encode(str));
}
 
const str = "This is GeeksForGeeks";
encodeStr();


Output

VGhpcyBpcyBHZWVrc0ZvckdlZWtz

Example 4: This examples encodes the string “VGhpcyBpcyBHZWVrc0ZvckdlZWtz” by creating a Base64 object.

Javascript




let Base64 = {
    _keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdef" +
        "ghijklmnopqrstuvwxyz0123456789+/=",
    encode: function (e) {
        let t = "";
        let n, r, i, s, o, u, a;
        let f = 0;
        e = Base64._utf8_encode(e);
        while (f < e.length) {
            n = e.charCodeAt(f++);
            r = e.charCodeAt(f++);
            i = e.charCodeAt(f++);
            s = n >> 2;
            o = (n & 3) << 4 | r >> 4;
            u = (r & 15) << 2 | i >> 6;
            a = i & 63;
            if (isNaN(r)) {
                u = a = 64
            } else if (isNaN(i)) {
                a = 64
            }
            t = t +
                this._keyStr.charAt(s) +
                this._keyStr.charAt(o) +
                this._keyStr.charAt(u) +
                this._keyStr.charAt(a)
        }
        return t
    },
    decode: function (e) {
        let t = "";
        let n, r, i;
        let s, o, u, a;
        let f = 0;
        e = e.replace(/[^A-Za-z0-9\+\/\=]/g, "");
        while (f < e.length) {
            s = this._keyStr.indexOf(e.charAt(f++));
            o = this._keyStr.indexOf(e.charAt(f++));
            u = this._keyStr.indexOf(e.charAt(f++));
            a = this._keyStr.indexOf(e.charAt(f++));
            n = s << 2 | o >> 4;
            r = (o & 15) << 4 | u >> 2;
            i = (u & 3) << 6 | a;
            t = t + String.fromCharCode(n);
            if (u != 64) {
                t = t + String.fromCharCode(r)
            }
            if (a != 64) {
                t = t + String.fromCharCode(i)
            }
        }
        t = Base64._utf8_decode(t);
        return t
    },
    _utf8_encode: function (e) {
        e = e.replace(/\r\n/g, "\n");
        let t = "";
        for (let n = 0; n < e.length; n++) {
            let r = e.charCodeAt(n);
            if (r < 128) {
                t += String.fromCharCode(r)
            } else if (r > 127 && r < 2048) {
                t +=
                    String.fromCharCode(r >> 6 | 192);
                t +=
                    String.fromCharCode(r & 63 | 128)
            } else {
                t +=
                    String.fromCharCode(r >> 12 | 224);
                t +=
                    String.fromCharCode(r >> 6 & 63 | 128);
                t +=
                    String.fromCharCode(r & 63 | 128)
            }
        }
        return t
    },
    _utf8_decode: function (e) {
        let t = "";
        let n = 0;
        let r = c1 = c2 = 0;
        while (n < e.length) {
            r = e.charCodeAt(n);
            if (r < 128) {
                t += String.fromCharCode(r);
                n++
            } else if (r > 191 && r < 224) {
                c2 = e.charCodeAt(n + 1);
                t +=
                    String.fromCharCode(
                        (r & 31) << 6 | c2 & 63);
                n += 2
            } else {
                c2 = e.charCodeAt(n + 1);
                c3 = e.charCodeAt(n + 2);
                t +=
                    String.fromCharCode(
                        (r & 15) << 12 |
                        (c2 & 63) << 6 | c3 & 63);
                n += 3
            }
        }
        return t
    }
}
 
function decodeStr() {
    console.log(Base64.decode(str));
}
 
const str = "VGhpcyBpcyBHZWVrc0ZvckdlZWtz";
decodeStr();


Output

This is GeeksForGeeks



Last Updated : 11 Aug, 2023
Like Article
Save Article
Previous
Next
Share your thoughts in the comments
Similar Reads