Merge Array of Objects by Same Key-Value

var arr = [
    {id: 1, tech_id:11, action: 'swim'},
    {id: 2, tech_id:11, action: 'run'},
    {id: 3, tech_id:22, action: 'climb'},
    {id: 4, tech_id:22, action: 'swim'},
    {id: 5, tech_id:11, action: 'jump'},
]

let mergeObj = arr.reduce((p, c) => {
    const {tech_id, ...otherData} = c;

    if (!(tech_id in p)) {
        p[tech_id] = {
            data: []
        }
    }
    
    p[tech_id].data.push(otherData)
    return p
}, {})

mergeObj = Object.keys(mergeObj).map(key => {
    return {
        tech_id: key,
        data: mergeObj[key].data
    }
})

console.log(mergeObj);

group the object in array by name

You can use forEach() for this.

let obj = [
    {
        name: "a",
        quantity: 2
    },
    {
        name: "b",
        quantity: 4
    },
    {
        name: "c",
        quantity: 88
    }
]

let obj2 = [
    {
        name: "a",
        quantity: 2
    }
]

obj.forEach((element)=>{
obj2.forEach((e)=>{
  if(element.name == e.name){
  element.quantity = element.quantity+e.quantity
    }
  })
})

console.log(obj);

const arr1 = [{ label: "one", value: "one", type: "arr1" }];
const arr2 = [{ label: "two", value: "two", type: "arr1" }];

console.log([...arr1, ...arr2]);