编辑代码

let arr=[
    {"key": "1737020577439", "projectName": "项目管理", "projectNumber": 5, }, 
    {"key": "1737020577441", "projectName": "需求开发及管理", "projectNumber": 23, },
    {"key": "1737020577443", "projectName": "系统设计", "projectNumber": 22, }
]

let arr1=[
    {
  "key": "1737020577439",
  "projectName": null,
  "projectNumber": "2",
  "projectDescription": null
}
]

let newArr=[];

arr.map(item=>{
    newArr.push(item);
    let match=arr1.filter(item1=>item.key == item1.key);
    if(match.length){
        newArr.push(...match)
    }
})

console.log(newArr)
// [
//     { key: "1737020577439", projectName: '项目管理', projectNumber: 5 },
//     {
//     key: "1737020577439",
//     projectName: null,
//     projectNumber: '2',
//     projectDescription: null
//   },
//   { key: "1737020577441", projectName: '需求开发及管理', projectNumber: 23 },
//   { key: "1737020577443", projectName: '系统设计', projectNumber: 22 }
// ]