js动态计算移动端rem值(remScale.js/flexible.js)--小技巧(推荐增强版-flexible.js)

设计稿的宽度/元素的宽度=手机屏幕/手机中元素的宽度

手机中元素的宽度=手机屏幕*元素的宽度/设计稿的宽度

 remScale.js文件

// JavaScript Document
; (function (doc, win) {
        var docEl = doc.documentElement,
            resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
            recalc = function () {
                var clientWidth = docEl.clientWidth;
                if (!clientWidth) return;
                if(clientWidth>=720){
                    docEl.style.fontSize = '100px';
                }else{
                    docEl.style.fontSize = 100 * (clientWidth / 720) + 'px';
                }
            };
        if (!doc.addEventListener) return;
        win.addEventListener(resizeEvt, recalc, false); //绑定事件
        doc.addEventListener('DOMContentLoaded', recalc, false);
		
})(document, window);

//==========================================================================
; (function (doc, win) {
    var docEl = doc.documentElement, // 获取html
        resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
        width = 1125, // 设计稿宽，用时只需要修改这一处
        recalc = function () {
            var clientWidth = docEl.clientWidth; // 获取设备尺寸
            if (!clientWidth) return; // 如果没有值，回去
            if (clientWidth > width) { // 如果超过设计稿宽度，就给一个固定值
                docEl.style.fontSize = '100px';
                docEl.style.width = width + 'px';
                docEl.style.margin = '0 auto';
            } else {
                docEl.style.fontSize = 100 * (clientWidth / width) + 'px';
            }
        };
    if (!doc.addEventListener) return; // 如果没有这个方法，回去
    win.addEventListener(resizeEvt, recalc, false); // 改变大小时调整一下
    doc.addEventListener('DOMContentLoaded', recalc, false); // 加载完成时调整
})(document, window);
// 使用时：1rem = 设计稿的宽度 / 100

flexible.js文件

(function(designWidth, maxWidth) {
	var doc = document,
	win = window,
	docEl = doc.documentElement,
	remStyle = document.createElement("style"),
	tid;

	function refreshRem() {
		var width = docEl.getBoundingClientRect().width;
		maxWidth = maxWidth || 540;
		width>maxWidth && (width=maxWidth);
		var rem = width * 100 / designWidth;
		remStyle.innerHTML = 'html{font-size:' + rem + 'px;}';
	}

	if (docEl.firstElementChild) {
		docEl.firstElementChild.appendChild(remStyle);
	} else {
		var wrap = doc.createElement("div");
		wrap.appendChild(remStyle);
		doc.write(wrap.innerHTML);
		wrap = null;
	}
	//要等 wiewport 设置好后才能执行 refreshRem，不然 refreshRem 会执行2次；
	refreshRem();

	win.addEventListener("resize", function() {
		clearTimeout(tid); //防止执行两次
		tid = setTimeout(refreshRem, 300);
	}, false);

	win.addEventListener("pageshow", function(e) {
		if (e.persisted) { // 浏览器后退的时候重新计算
			clearTimeout(tid);
			tid = setTimeout(refreshRem, 300);
		}
	}, false);

	if (doc.readyState === "complete") {
		doc.body.style.fontSize = "16px";
	} else {
		doc.addEventListener("DOMContentLoaded", function(e) {
			doc.body.style.fontSize = "16px";
		}, false);
	}
})(750, 750);

增强版-flexible.js

(function(win, lib) {
  var doc = win.document;
  var docEl = doc.documentElement;
  var metaEl = doc.querySelector('meta[name="viewport"]');
  var flexibleEl = doc.querySelector('meta[name="flexible"]');
  var dpr = 0;
  var scale = 0;
  var tid;
  var flexible = lib.flexible || (lib.flexible = {});

  if (metaEl) {
    console.warn("将根据已有的meta标签来设置缩放比例");
    var match = metaEl
      .getAttribute("content")
      // eslint-disable-next-line no-useless-escape
      .match(/initial\-scale=([\d\.]+)/);
    if (match) {
      scale = parseFloat(match[1]);
      dpr = parseInt(1 / scale);
    }
  } else if (flexibleEl) {
    var content = flexibleEl.getAttribute("content");
    if (content) {
      // eslint-disable-next-line no-useless-escape
      var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);
      // eslint-disable-next-line no-useless-escape
      var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);
      if (initialDpr) {
        dpr = parseFloat(initialDpr[1]);
        scale = parseFloat((1 / dpr).toFixed(2));
      }
      if (maximumDpr) {
        dpr = parseFloat(maximumDpr[1]);
        scale = parseFloat((1 / dpr).toFixed(2));
      }
    }
  }

  if (!dpr && !scale) {
    // eslint-disable-next-line no-unused-vars
    var isAndroid = win.navigator.appVersion.match(/android/gi);
    var isIPhone = win.navigator.appVersion.match(/iphone/gi);
    var devicePixelRatio = win.devicePixelRatio;
    if (isIPhone) {
      // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案
      if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {
        dpr = 3;
      } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)) {
        dpr = 2;
      } else {
        dpr = 1;
      }
    } else {
      // 其他设备下，仍旧使用1倍的方案
      dpr = 1;
    }
    scale = 1 / dpr;
  }

  docEl.setAttribute("data-dpr", dpr);
  if (!metaEl) {
    metaEl = doc.createElement("meta");
    metaEl.setAttribute("name", "viewport");
    metaEl.setAttribute(
      "content",
      "initial-scale=" +
        scale +
        ", maximum-scale=" +
        scale +
        ", minimum-scale=" +
        scale +
        ", user-scalable=no"
    );
    if (docEl.firstElementChild) {
      docEl.firstElementChild.appendChild(metaEl);
    } else {
      var wrap = doc.createElement("div");
      wrap.appendChild(metaEl);
      doc.write(wrap.innerHTML);
    }
  }

  function refreshRem() {
    var width = docEl.getBoundingClientRect().width;
    // 最小1366px，最大适配2560px
    if (width / dpr < 1366) {
      width = 1366 * dpr;
    } else if (width / dpr > 2560) {
      width = 2560 * dpr;
    }
    // 设置成24等份，设计稿时1920px的，这样1rem就是80px
    var rem = width / 24;
    docEl.style.fontSize = rem + "px";
    flexible.rem = win.rem = rem;
  }

  win.addEventListener(
    "resize",
    function() {
      clearTimeout(tid);
      tid = setTimeout(refreshRem, 300);
    },
    false
  );
  win.addEventListener(
    "pageshow",
    function(e) {
      if (e.persisted) {
        clearTimeout(tid);
        tid = setTimeout(refreshRem, 300);
      }
    },
    false
  );

  if (doc.readyState === "complete") {
    doc.body.style.fontSize = 12 * dpr + "px";
  } else {
    doc.addEventListener(
      "DOMContentLoaded",
      // eslint-disable-next-line no-unused-vars
      function(e) {
        doc.body.style.fontSize = 12 * dpr + "px";
      },
      false
    );
  }

  refreshRem();

  flexible.dpr = win.dpr = dpr;
  flexible.refreshRem = refreshRem;
  flexible.rem2px = function(d) {
    var val = parseFloat(d) * this.rem;
    if (typeof d === "string" && d.match(/rem$/)) {
      val += "px";
    }
    return val;
  };
  flexible.px2rem = function(d) {
    var val = parseFloat(d) / this.rem;
    if (typeof d === "string" && d.match(/px$/)) {
      val += "rem";
    }
    return val;
  };
})(window, window["lib"] || (window["lib"] = {}));

---

设计稿比例换算
const DEFAULT_DENSITY = 1
const defaultWidthS = 375
export const deviceWidth = Dimensions.get("window").width


//375比例方法
export function fitSize(size: number | undefined) {
  if (size === undefined) return 0
  return (size / DEFAULT_DENSITY) * (deviceWidth / defaultWidthS)
}