How do I merge array of Objects but unshift array in JavaScript -

i merge these 2 array of objects urls use unshift merge arrays instead of replacing.

here's example

var arr1 = [{   "keyword": "name",   "score": 0.8992112752974006,   "urls": ["url1"],   "ids": ["5748bf9ab58adb2f614da195"] }, {   "keyword": "name1",   "score": 0.39953909596222775,   "urls": ["url2"],   "ids": ["5743260055f979a31fa98971"] }, {   "keyword": "name3",   "score": 0.4960953181766197,   "urls": ["url4"],   "ids": ["58c04cd5208b4945c3920cad"] }, {   "keyword": "name4",   "score": 0.3337163443410707,   "urls": ["url5"],   "ids": ["573628c38e32eeb039377f7e"] }];  var arr2 = [{   "keyword": "name",   "score": 0.8992112752974006,   "urls": ["url6"],   "ids": [""] }, {   "keyword": "name1",   "score": 0.39953909596222775,   "urls": ["url7"],   "ids": [""] }] 

i result

[{   "keyword": "name",   "score": 0.8992112752974006,   "urls": ["url6", "url1"],   "ids": ["5748bf9ab58adb2f614da195"] }, {   "keyword": "name1",   "score": 0.39953909596222775,   "urls": ["url7", "url2"],   "ids": ["5743260055f979a31fa98971"] }, {   "keyword": "name3",   "score": 0.4960953181766197,   "urls": ["url4"],   "ids": ["58c04cd5208b4945c3920cad"] }, {   "keyword": "name4",   "score": 0.3337163443410707,   "urls": ["url5"],   "ids": ["573628c38e32eeb039377f7e"] }];     

here's attempt result replace array of urls;

var a3 = arr1.concat(arr2).reduce((acc, x) => {   acc[x.keyword] = object.assign(acc[x.keyword] || {}, x);   return acc; }, {}); console.log(a3); 

it urls merged. other values overridden.

you use map collecting objects same keyword , update if necessary. solution works arbitrary count of arrays.

var array1 = [{ keyword: "name", score: 0.8992112752974006, urls: ["url1"], ids: ["5748bf9ab58adb2f614da195"] }, { keyword: "name1", score: 0.39953909596222775, urls: ["url2"], ids: ["5743260055f979a31fa98971"] }, { keyword: "name3", score: 0.4960953181766197, urls: ["url4"], ids: ["58c04cd5208b4945c3920cad"] }, { keyword: "name4", score: 0.3337163443410707, urls: ["url5"], ids: ["573628c38e32eeb039377f7e"] }],      array2 = [{ keyword: "name", score: 0.8992112752974006, urls: ["url6"], ids: [""] }, { keyword: "name1", score: 0.39953909596222775, urls: ["url7"], ids: [""] }],      map = new map,      result = [],      fn = => {          if (map.has(a.keyword)) {              map.get(a.keyword).urls.unshift(...a.urls);              return;          }          map.set(a.keyword, a);          result.push(a);      };    [array1, array2].foreach(a => a.foreach(fn));    console.log(result);

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