这个问题我昨天刚好碰到，解决了。其实就是vant组件里的那个common文件夹里的utils.js。你的utils.js文件夹没有addUnit这个方法，所以才会报这个错。去github上下一个最新版的vant组件的包，把lib或者dist下的common的utils.j粘过去就好了（要粘有addUnit方法的）
我这儿也把utils.js的内容附上了。
"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
function isDef(value) {
return value !== undefined && value !== null;
}
exports.isDef = isDef;
function isObj(x) {
var type = typeof x;
return x !== null && (type === 'object' || type === 'function');
}
exports.isObj = isObj;
function isNumber(value) {
return /^\d+(\.\d+)?$/.test(value);
}
exports.isNumber = isNumber;
function range(num, min, max) {
return Math.min(Math.max(num, min), max);
}
exports.range = range;
function nextTick(fn) {
setTimeout(function () {
fn();
}, 1000 / 30);
}
exports.nextTick = nextTick;
var systemInfo = null;
function getSystemInfoSync() {
if (systemInfo == null) {
systemInfo = wx.getSystemInfoSync();
}
return systemInfo;
}
exports.getSystemInfoSync = getSystemInfoSync;
function addUnit(value) {
if (!isDef(value)) {
return undefined;
}
value = String(value);
return isNumber(value) ? value + "px" : value;
}
exports.addUnit = addUnit;