Inserting data in custom list using javascript in SharePoint 2013

1. Create a SharePoint custom list : For an example such as below one

2. Create a javascript file and copy below code into that file.

function SaveVehicle() {

    var listName = "vehicleList";
    var newVINNumber = document.getElementById('txtVINNumber').value;
    var newVehicleYear = document.getElementById('txtVehicleYear').value;
    var newPlateID = document.getElementById('txtPlateID').value;
    var newCurrentMileage = document.getElementById('txtCurrentMileage').value;
   

    CreateListItemWithDetails(listName, _spPageContextInfo.webAbsoluteUrl, newVINNumber, newVehicleYear,
        newPlateID,newCurrentMileage, function () {
        console.log("New Item has been created successfully.");
    }, function () {
        console.log("Ooops, an error occured. Please try again.");
    });
}

function CreateListItemWithDetails(listName, webUrl, newVINNumber, newVehicleYear,
        newPlateID,newCurrentMileage, success, failure) {
    var itemType = GetItemTypeForListName(listName);
    var item = {
        "__metadata": { "type": itemType },
        "VINNumber": newVINNumber,
        "VehicleYear": newVehicleYear,
        "PlateID": newPlateID,
        "CurrentMileage" : newCurrentMileage
    };

    $.ajax({
        url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getbytitle('" + listName + "')/items",
        type: "POST",
        contentType: "application/json;odata=verbose",
        data: JSON.stringify(item),
        headers: {
            "Accept": "application/json;odata=verbose",
            "X-RequestDigest": $("#__REQUESTDIGEST").val()
        },
        success: function (data) {
            success(data);
        },
        error: function (data) {
            failure(data);
        }
    });
}

function GetItemTypeForListName(name) {
    return "SP.Data." + name.charAt(0).toUpperCase() + name.split(" ").join("").slice(1) + "ListItem";
}

3. Add a "Script Editor" or "Content Editor" Web Part and Add this line of code on clicking of submit button
Include the javascript file which is in step 2 with script tag.

<button onclick="SaveVehicle()">Submit</button>


You can use "Developer Tools" of Browser or "Start Debugging" from Visual Studio to