// Html file

<template>
    <!-- lightning button for open modal window -->
    <lightning-button variant="brand" label="Add New Work Order" title="What is Modal/PopUp in LWC?" onclick={openModal}
    class="slds-float_right">
    </lightning-button>

// JS code

   openModal() {
        // to open modal set isModalOpen tarck value as true             
        this.fetchStandardWorkOrders();
    }

fetchStandardWorkOrders(){
        getStandardWorkOrders({})
        .then(res=> {
            let generalarray = [];
            let specailtyWO = [];
            let customNamedWO = [];
            res.forEach(element => {
                    if(element.Type__c == 'Standard'){
                        generalarray.push(element);
                    }
                    else if(element.Type__c == 'Specialty'){
                        specailtyWO.push(element);
                    }
                    else if(element.Type__c == 'Custom Named'){
                        customNamedWO.push(element);
                    }
                });           
            this.generalarray = generalarray;
            this.customNamedWO = customNamedWO;
            this.specailtyWO = specailtyWO;
            this.isModalOpen = true;   
        })
        .catch(err=> {
            console.log(err);
        })
    }