fupin/utils/base64.js

/**
* UTF16和UTF8转换对照表
* U+00000000 – U+0000007F 	0xxxxxxx
* U+00000080 – U+000007FF 	110xxxxx 10xxxxxx
* U+00000800 – U+0000FFFF 	1110xxxx 10xxxxxx 10xxxxxx
* U+00010000 – U+001FFFFF 	11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
* U+00200000 – U+03FFFFFF 	111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
* U+04000000 – U+7FFFFFFF 	1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
*/
//外部js引用时这样写：import {Base64} from '/xxx/base64';//路径需要根据实际路径去写
export let Base64 = {
	// 转码表
	tables : [
			'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
			'I', 'J', 'K', 'L', 'M', 'N', 'O' ,'P',
			'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
			'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
			'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
			'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
			'w', 'x', 'y', 'z', '0', '1', '2', '3',
			'4', '5', '6', '7', '8', '9', '+', '/'
	],
	UTF16ToUTF8 : function (str) {
		let results = [], len = str.length;
		for (let i = 0; i < len; i++) {
			let code = str.charCodeAt(i);
			if (code > 0x0000 && code <= 0x007F) {
				/* 一字节，不考虑0x0000，因为是空字节
				   U+00000000 – U+0000007F 	0xxxxxxx
				*/
				results.push(str.charAt(i));
			} else if (code >= 0x0080 && code <= 0x07FF) {
				/* 二字节
				   U+00000080 – U+000007FF 	110xxxxx 10xxxxxx
				   110xxxxx
				*/
				let byte1 = 0xC0 | ((code >> 6) & 0x1F);
				// 10xxxxxx
				let byte2 = 0x80 | (code & 0x3F);
				results.push(
					String.fromCharCode(byte1), 
					String.fromCharCode(byte2)
				);
			} else if (code >= 0x0800 && code <= 0xFFFF) {
				/* 三字节
				   U+00000800 – U+0000FFFF 	1110xxxx 10xxxxxx 10xxxxxx
				   1110xxxx
				*/
				let byte1 = 0xE0 | ((code >> 12) & 0x0F);
				// 10xxxxxx
				let byte2 = 0x80 | ((code >> 6) & 0x3F);
				// 10xxxxxx
				let byte3 = 0x80 | (code & 0x3F);
				results.push(
					String.fromCharCode(byte1), 
					String.fromCharCode(byte2), 
					String.fromCharCode(byte3)
				);
			} else if (code >= 0x00010000 && code <= 0x001FFFFF) {
				// 四字节
				// U+00010000 – U+001FFFFF 	11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
			} else if (code >= 0x00200000 && code <= 0x03FFFFFF) {
				// 五字节
				// U+00200000 – U+03FFFFFF 	111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
			} else /** if (code >= 0x04000000 && code <= 0x7FFFFFFF)*/ {
				// 六字节
				// U+04000000 – U+7FFFFFFF 	1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
			}
		}

		return results.join('');
	},
	UTF8ToUTF16 : function (str) {
		let results = [], len = str.length;
		let i = 0;
		for (let i = 0; i < len; i++) {
			let code = str.charCodeAt(i);
			// 第一字节判断
			if (((code >> 7) & 0xFF) == 0x0) {
				// 一字节
				// 0xxxxxxx
				results.push(str.charAt(i));
			} else if (((code >> 5) & 0xFF) == 0x6) {
				// 二字节
				// 110xxxxx 10xxxxxx
				let code2 = str.charCodeAt(++i);
				let byte1 = (code & 0x1F) << 6;
				let byte2 = code2 & 0x3F;
				let utf16 = byte1 | byte2;
				results.push(Sting.fromCharCode(utf16));
			} else if (((code >> 4) & 0xFF) == 0xE) {
				// 三字节
				// 1110xxxx 10xxxxxx 10xxxxxx
				let code2 = str.charCodeAt(++i);
				let code3 = str.charCodeAt(++i);
				let byte1 = (code << 4) | ((code2 >> 2) & 0x0F);
				let byte2 = ((code2 & 0x03) << 6) | (code3 & 0x3F);
				let utf16 = ((byte1 & 0x00FF) << 8) | byte2
				results.push(String.fromCharCode(utf16));
			} else if (((code >> 3) & 0xFF) == 0x1E) {
				// 四字节
				// 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
			} else if (((code >> 2) & 0xFF) == 0x3E) {
				// 五字节
				// 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
			} else /** if (((code >> 1) & 0xFF) == 0x7E)*/ {
				// 六字节
				// 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
			}
		}

		return results.join('');
	},
	encode : function (str) {
		if (!str) {
			return '';
		}
		let utf8    = this.UTF16ToUTF8(str); // 转成UTF-8
		let i = 0; // 遍历索引
		let len = utf8.length;
		let results = [];
		while (i < len) {
			let c1 = utf8.charCodeAt(i++) & 0xFF;
			results.push(this.tables[c1 >> 2]);
			// 补2个=
			if (i == len) {
				results.push(this.tables[(c1 & 0x3) << 4]);
				results.push('==');
				break;
			}
			let c2 = utf8.charCodeAt(i++);
			// 补1个=
			if (i == len) {
				results.push(this.tables[((c1 & 0x3) << 4) | ((c2 >> 4) & 0x0F)]);
				results.push(this.tables[(c2 & 0x0F) << 2]);
				results.push('=');
				break;
			}
			let c3 = utf8.charCodeAt(i++);
			results.push(this.tables[((c1 & 0x3) << 4) | ((c2 >> 4) & 0x0F)]);
			results.push(this.tables[((c2 & 0x0F) << 2) | ((c3 & 0xC0) >> 6)]);
			results.push(this.tables[c3 & 0x3F]);
		}

		return results.join('');
	},
	decode : function (str) {
		//判断是否为空
		if (!str) {
			return '';
		}

		let len = str.length;
		let i   = 0;
		let results = [];
		//循环解出字符数组
		while (i < len) {
			let	code1 = this.tables.indexOf(str.charAt(i++));
			let code2 = this.tables.indexOf(str.charAt(i++));
			let code3 = this.tables.indexOf(str.charAt(i++));
			let code4 = this.tables.indexOf(str.charAt(i++));

			let c1 = (code1 << 2) | (code2 >> 4);
			results.push(String.fromCharCode(c1));

			if (code3 != -1) {
				let c2 = ((code2 & 0xF) << 4) | (code3 >> 2);
				results.push(String.fromCharCode(c2));
			}
			if (code4 != -1) {
				let c3 = ((code3 & 0x3) << 6) | code4;
				results.push(String.fromCharCode(c3));
			}

		}

		return this.UTF8ToUTF16(results.join(''));
	}
};