javascript 常用函数

将 base64 字符串转换成文件

function base64ToFile (b64Data, contentType) {
contentType = contentType || ''
const sliceSize = 512
const byteCharacters = atob(b64Data)
const byteArrays = []
for (let offset = 0; offset < byteCharacters.length; offset += sliceSize) {
const slice = byteCharacters.slice(offset, offset + sliceSize)
const byteNumbers = new Array(slice.length)
for (let i = 0; i < slice.length; i++) {
byteNumbers[ i ] = slice.charCodeAt(i)
}
const byteArray = new Uint8Array(byteNumbers)
byteArrays.push(byteArray)
}
return new File(byteArrays, 'image.png', { type: contentType })
}

打印日志

function _log(info) {
var loggerDom = document.querySelector("#logger");
var loggerTitle = null;
if(!loggerDom) {
loggerDom = document.createElement("div");
loggerDom.id = "logger";
loggerTitle = document.createElement("p");
loggerTitle.innerHTML = "日志标题:";
loggerTitle.style.cssText = "color:blue;font-weight:bold";
loggerDom.appendChild(loggerTitle);
document.querySelector("body").appendChild(loggerDom);
}
var pDom = document.createElement("p");
pDom.innerHTML = new Date().toISOString() + ":<span style='color:red;font-weight:bold;'>" + info + "</span>";
loggerDom.insertBefore(pDom, loggerDom.childNodes[1]);
}

显示精确到天的倒计时

/**
* 显示精确到天的倒计时
* @param timeStr 日期字符串，格式：2017年04月30日09时00分11秒
* @param currDate 当前时间的 Date 对象
*/
function showCountdownAccurateToDate (timeStr, currDate) {
const TOTAL_TIME_FOR_SECOND = 1000
const TOTAL_TIME_FOR_MINUTE = TOTAL_TIME_FOR_SECOND * 60
const TOTAL_TIME_FOR_HOUR = TOTAL_TIME_FOR_MINUTE * 60
const TOTAL_TIME_FOR_DAY = TOTAL_TIME_FOR_HOUR * 24
let time = new Date(timeStr.replace(/[年月]/g, '/').replace(/[日秒]/g, ' ').replace(/[时分秒]/g, ':').substring(0, 19)).getTime()
let nowTime = currDate.getTime()
let timeDiff = time - nowTime
let showStr = []
if (time - nowTime > 0) {
let day = parseInt(timeDiff / TOTAL_TIME_FOR_DAY)
let hour = parseInt((timeDiff - day * TOTAL_TIME_FOR_DAY) / TOTAL_TIME_FOR_HOUR)
let minute = parseInt((timeDiff - day * TOTAL_TIME_FOR_DAY - hour * TOTAL_TIME_FOR_HOUR) / TOTAL_TIME_FOR_MINUTE)
let second = parseInt((timeDiff - day * TOTAL_TIME_FOR_DAY - hour * TOTAL_TIME_FOR_HOUR - minute * TOTAL_TIME_FOR_MINUTE) / TOTAL_TIME_FOR_SECOND)
showStr.push(day + '天')
showStr.push(hour + '时')
showStr.push(minute + '分')
showStr.push(second + '秒')
return showStr.join('')
} else {
return timeStr
}
}