ECMQAScript: This is the core of js, equivalent to the virtual machine of java, responsible for interpreting the code
DOM: DocumentObject Model, which represents the ability of js to manipulate HTML.
BOM: Broswer Object Model, which represents the ability of js to operate the browser
variable:
1. Judgment of variable type in js, typeof(a);
2. Before a variable is assigned a value, its type is undefined.
Conversion of strings to numbers:
1. String to integer conversion
The main method:
parseInt() converts a string to an integer
isNAN() determines whether a string is a number
For example, to implement the sum of two strings:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>字符串转成整数</title>
<script>
window.onload = function () {
var oInput1 = document.getElementById('input1');
var oInput2 = document.getElementById('input2');
var oBuuton1 = document.getElementById('button1');
oBuuton1.onclick = function () {
if (isNaN(oInput1.value) == true) {
alert('请在第一个框输入数字');
} else if (isNaN(oInput2.value) == true) {
alert('请在第二个框输入数字');
} else {
var iAnswer = parseInt(oInput1.value) + parseInt(oInput2.value);
alert(iAnswer);
}
}
}
</script>
</head>
<body>
<input type="text" id="input1">
<input type="text" id="input2">
<input type="button" id="button1" value="求和">
</body>
</html>2. String and decimal conversion
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>字符串转成整数</title>
<script>
window.onload = function () {
var oInput1 = document.getElementById('input1');
var oInput2 = document.getElementById('input2');
var oBuuton1 = document.getElementById('button1');
oBuuton1.onclick = function () {
if (isNaN(oInput1.value) == true) {
alert('请在第一个框输入数字');
} else if (isNaN(oInput2.value) == true) {
alert('请在第二个框输入数字');
} else {
// var iAnswer = parseInt(oInput1.value) + parseInt(oInput2.value);
var iAnswer = parseFloat(oInput1.value) + parseFloat(oInput2.value);
alert(iAnswer);
}
}
}
</script>
</head>
<body>
<input type="text" id="input1">
<input type="text" id="input2">
<input type="button" id="button1" value="求和">
</body>
</html>The difference between "==" and "===":
"==" is first converted to the same type before comparison
"===" does not convert the type and compares directly
Note: The problem of subtracting two strings
The subtraction of two strings will first convert the type before subtracting
Hungarian notation:
Type prefix:
capitalized