Introduction to String-digital methods in JavaScript

We know that the simplest way to spin a digital string is:

Force type conversions

To convert integers to strings, you must use the integer.tostring () static method or the String.valueof () static method to convert the string to an integer, and you must use Integer.valueof ().
As you can see, type conversions in JavaScript cannot be viewed as "coercion type conversions".

You can also use coercion type conversion (type casting) to handle the type of the converted value. You can use coercion type conversions to access a specific value, even if it is of another type.
The 3 mandatory type conversions available in ECMAScript are as follows:
Boolean (value)--converts a given value to a Boolean;
Number (value)-Converts a given value to a digit (can be an integer or floating point);
String (value)--converts the given value to a string.
Converting a value with one of these three functions creates a new value that holds the value directly converted from the original value. This can have unintended consequences.
The Boolean () function returns True when the value to be converted is a string with at least one character, a number other than 0 digits, or an object (which is discussed in the next section). If the value is an empty string, number 0, undefined, or null, it returns FALSE.

You can use the following code snippet to test a Boolean type cast.

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Boolean ("") ;  //false  –   empty   string Boolean ("Hi");  //true   –   non-empty   string Boolean (m);  //true  –   non-zero   number Boolean (null);  //false  -   null Boolean (0);   //false  -   Zero Boolean (new   Object ());  //true & nbsp –   object

The force type conversion of number () is similar to the parseint () and parsefloat () methods, except that it converts the entire value, not the partial value. Remember, the parseint () and parsefloat () methods only convert the string before the first invalid character, so "4.5.6" is converted to "4.5". Force type conversion with number (), and "4.5.6" returns Nan, because the entire string value cannot be converted to numbers. If the string value can be completely converted, number () will determine whether to call the parseint () method or call the Parsefloat () method. The following table describes what happens when you call the number () method on a different value:

Usage results
Number (false) 0
Number (TRUE) 1
Number (undefined) NaN
Number (NULL) 0
Number ("5.5") 5.5
Number ("56") 56
Number ("5.6.7") NaN
Number (new Object ()) NaN
Number (100) 100

The code is as follows:

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<div style= "Background-color: #FFCC99; width:400px; margin:0px; padding:5px" <script language= " JavaScript "type=" Text/javascript Function Checkform () {         var Age2;     age2 = number (Document.frmTest.age.value) + 1;     document.frmTest.age2.value = age2;    /*     var Salesforce_para;     Salesforce_para = "name=" + document.frmTest.name.value;     Salesforce_para + + + "&" + "age=" + document.frmTest.age.value;     var targeturl = "test_js.php?" + Salesforce_para;     window.location = TargetUrl;     */ } </script> <form action= "test_js.php" method= "post" name= "Frmtest" > <!--name: <input type= "text" name= "name" ><br/>--> Ages: <input type= "text" name= "age" ><br/> <input type= "button" name= "Submit" value= "Submit->> View Something" onclick= "Checkform ()" ><br Something: <input type= "text" name= "Age2" > </form> </div>

Strings can only be additive (stitching)

string addition (stitching) is very common, but the string for subtraction, multiplication, division?

This seems to be difficult to define, in fact, there is no subtraction, multiplication, division operation of Strings.

But JavaScript is a dynamic language, and if you take these three actions with two strings, he will try to turn them into numbers and then do the appropriate action. For example:

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Alert ("45"-"32"); 13alert ("5" * "6"); 30alert ("12"/"3"); 4

But this conversion operation is not much like parseint and parsefloat, and it is similar to number, for example:

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Alert ("123a"-"2BC"); NaN Alert (parseint ("123a")-parseint ("2BC")); 121 Alert (Number ("123a")-Number ("2BC"));

Nan that is, this conversion, like number, converts the impure numeric string to Nan, indicating that it is not a number.

And parseint, Parsefloat takes out the string to take out the front can be expressed as a number of parts, and ignore the following can not be expressed as a number of parts.

The most concise method of string digital

By using a string to perform an operation that it cannot do, you first try to turn the attribute into a number. We can convert a string to a number by adding a positive symbol to the string. Such as:

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var num = + "45"; Alert (typeof num); There is an application of this method in Numberjquery, for example, how do we get a string to determine if he has only numbers? The jquery approach: var string = "321"; This thing gets the string and what is at random Alert (+string + "" = = string); True means a numeric string, otherwise there are other ways to take advantage of this feature, such as: var num = "45"-0; Alert (typeof num); Numbervar num = "45" * 1; Alert (typeof num); Numbervar num = "45"/1; Alert (typeof num); Number

For example, if you want to convert the string "1234blue" to an integer, then parseint () will return 1234, because when it detects character B, it stops the detection process. The literal number contained in the string is converted to numbers correctly, so the string "0xA" is correctly converted to Number 10. However, the string "22.5" will be converted to 22 because the decimal point is an invalid character for an integer. Some examples are as follows:

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parseint ("1234blue"); Returns 1234 parseint ("0xA"); Returns 10 parseint ("22.5"); Returns 22 parseint ("Blue"); Returns NaN

The parseint () method also has a base pattern that converts binary, octal, hexadecimal, or any other string of strings into integers. The base is specified by the second parameter of the parseint () method, so to parse the hexadecimal value, you call the parseint () method as follows:

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parseint ("AF", 16); Returns 175

Of course, for binary, octal, or even decimal (default mode), you can call the parseint () method:

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parseint ("10", 2); Returns 2 parseint ("10", 8); Returns 8 parseint ("10", 10); Returns 10

If the decimal number contains a leading 0, it is best to use cardinality 10 so that you do not accidentally get the octal value. For example:

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parseint ("010"); Returns 8 parseint ("010", 8); Returns 8 parseint ("010", 10); Returns 10

In this code, two lines of code parse the string "010" into a number. The first line of code regards this string as a octal value, parsing it in the same way as the second line of code (the Declaration cardinality is 8). The last line of code declares a cardinality of 10, so the iNum3 finally equals 10.

System issues

The 0x starts with 16, so both number and parseint convert the 16 binary, and so does the automatic conversion of the string:

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Alert (parseint ("0x10")); 16 Alert (Number ("0x10")); 16 Alert (+ "0x10");

16 but parsefloat some awkward, he does not know 16, the result becomes this:

Alert (parsefloat ("0x10")); 0 More tragic is the beginning of the 0, we know that 0 can be used to represent 8, in number and string automatic conversion, 0 start as a decimal to get, such as:

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Alert (Number ("010")); 10 Alert (+ "010"); 10 and parseint is very sad reminders, ECMAScript did not make this mandatory so the following situation occurred: Alert (parseint ("010")); 8 in Firefox & Iealert (parseint ("010"));

Ten in Chrome? (?_?)? No wonder it's rare to see 8 in JavaScript, and if you want to make sure that 8 can only use parseint's second argument:

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Alert ( parseint ("010", 8)); 8parseFloat continues to not recognize 8, so: Alert (parsefloat ("010"));//10