31 lines
900 B
JavaScript
31 lines
900 B
JavaScript
"use strict";
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const $ = selector => document.querySelector(selector);
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const getErrorMsg = lbl => `${lbl} must be a valid number greater than zero.`;
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const focusAndSelect = selector => {
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const elem = $(selector);
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elem.focus();
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elem.select();
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};
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const processEntries = () => {
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const miles = parseFloat($("#miles").value);
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const gallons = parseFloat($("#gallons").value);
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if (isNaN(miles) || miles <= 0) {
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alert(getErrorMsg("Miles driven"));
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focusAndSelect("#miles");
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} else if (isNaN(gallons) || gallons <= 0) {
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alert(getErrorMsg("Gallons of gas used"));
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focusAndSelect("#gallons");
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} else {
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$("#mpg").value = (miles / gallons).toFixed(2);
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}
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};
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document.addEventListener("DOMContentLoaded", () => {
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$("#calculate").addEventListener("click", processEntries);
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$("#miles").focus();
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}); |