---------------------js file-----------------------------
import { LightningElement, track } from 'lwc';
import getOppList from '@salesforce/apex/customSearchController.getOppList';
import {ShowToastEvent} from 'lightning/platformShowToastEvent'
export default class CustomSearch extends LightningElement {
    @track opportunity;
    sVal='';
    receivedMessage;
    @track record = [];
    @track columns=[
        {label: 'Name', fieldName: 'Name',type: 'url', 
        typeAttributes: { 
            label: {
                fieldName: 'Name'
            } 
        },
        sortable: true },
          {label: 'Account Name', fieldName: 'AccountId',type: 'url', 
        typeAttributes: { 
            label: {
                fieldName: 'AccountId.Name'
            } 
        }, 
        sortable: true},
        {label: 'Stage Name', fieldName: 'StageName',type: 'picklist'},
        {label: 'Type', fieldName: 'Type',type: 'picklist'},
        {label: 'Amount', fieldName: 'Amount',type: 'currency'},
        {label:'Action',type:'button',typeAttributes: {
            label: 'Send Opp',
            name: 'Send',
            disabled: false,
            value: 'send',
            iconPosition: 'left'
        }
    }
    ];
    // update sVal var when input field value change
    updateSeachKey(event) {
        this.sVal = event.target.value;
    }
 
    // call apex method on button click 
    handleSearch() {
        // if search input value is not blank then call apex method, else display error msg 
        if (this.sVal !== '') {
            getOppList({
                    searchKey: this.sVal
                })
                .then(result => {
                    // set @track opportunities variable with return contact list from server  
                    this.opportunity = result;
                })
                .catch(error => {
                    // display server exception in toast msg 
                    const event = new ShowToastEvent({
                        title: 'Error',
                        variant: 'error',
                        message: error.body.message,
                    });
                    this.dispatchEvent(event);
                    // reset contacts var with null   
                    this.opportunity = null;
                });
        } else {
            // fire toast event if input field is blank
            const event = new ShowToastEvent({
                variant: 'error',
                message: 'Search text missing..',
            });
            this.dispatchEvent(event);
        }
    }
    handleRowAction(event){
        const row = event.detail.row;
        let actionName = event.detail.action.name;
        switch(actionName) {
            case 'Send':
            this.record = row;
            const calloutURI = 'https://herokuapp.com';
            fetch(calloutURI, {
                method: "POST",
                headers: {
                    "Accept": "application/json"
                  },
                  body:  JSON.stringify(record)
            })
            .then((response) => {
                       return response.json(); 
                })
                .then(responseJSON => {
                    console.log(responseJSON);
                    console.log(record);
                })
                .catch(error => {
                    const event = new ShowToastEvent({
                        title: 'Error',
                        variant: 'error',
                        message: error.body.message,
                    });
                    this.dispatchEvent(event);
                });
        }
    }
}
-------------------html file---------------------------
<template>
   <div class="slds-m-around_medium">
     
        <div class="slds-m-bottom_small">
            <lightning-input type="text"
               value={sVal}
               label="Search Opportunity"
               onchange={updateSeachKey}
               ></lightning-input>
         </div>
         
         <lightning-button label="Search"
            onclick={handleSearch}
            variant="brand"></lightning-button>
            
            <lightning-datatable data={opportunity} columns={columns} key-field="id" onrowaction={handleRowAction}>
            </lightning-datatable>
</div>
</template>