Learn JavaScript notes (1)-Basics

Here, just write down important things! This chapter is the foundation of the Foundation!

[Javascript]
<Script language = "javaScript">
// The undefined value is actually derived from the null value. Therefore, ECMAScript defines them as equal.
Alert (null = undefined); // output: true;
// Remove string Spaces
Var strings = "'Day to day '";
Alert (trimFunction (strings ));

/*
* Removes all spaces in the string.
*/
Function trimFunction (str ){
Return str. replace (/\ s/g ,"");
}
</Script>

[Html]
<Script language = "javaScript">
/*
* Determines whether a number is used.
* If the value is true, the variable value is not a number.
* If the value is false, the variable value is a number.
*/
Alert (isNaN ("fdsa "));
 
/*
* Obtain the length of a string.
*/
Alert ("saffdsa". length );
 
/*
* ToString () method of javaScript
*/
Var iNumber = 10.6;
Alert (iNumber. toString (2); // binary
Alert (iNumber. toString (8); // octal
Alert (iNumber. toString (); // default decimal
Alert (iNumber. toString (16); // hexadecimal
</Script>

 

Conversion of javaScript values:
[Javascript]
/*
* JavaScript numeric Conversion
* ParseInt/parseFloat
* The parseInt () method first checks the character at position 0 and determines whether it is a valid number. If not, NaN is returned
* Do not perform other operations. If yes, view the 1 character and perform the same test. This process continues until the characters of the invalid number are reached!
* In this case, parseInt converts the string before the character to a number.
* For example, if you want to convert the string "1234 bule" to a number, parseInt returns 1234 because when it detects B, the detection process is stopped,
* The number literal contained in the string is correctly converted to a number.
* If you want to convert to hexadecimal, or 8 or 2:
* ParseInt ("AF", 16); parseInt ("010", 8 );
*/
// Alert (parseInt ("1234 bule "));
// Alert (parseInt ("0xA "));
// Alert (parseInt ("22.5 "));
// Alert (parseInt ("bule "));
// Alert ("Convert:" + parseInt ("0010", 10 ));
// Alert (parseInt ("0 "));

/**
* Forced type conversion:
* Number (value) converts a specified value to a Number (which can be an integer or floating point Number)
* Boolean (value) converts the specified value to the Boolean type.
* String (value) converts a specified value to a String
* Use one of the three functions to convert the value and store the new value directly converted from the original value. This will cause abnormal noise!
*
*/
Alert (Number ("0010.23 "));
Number Type:
[Javascript]
/**
* Number class
* The toFixed () method parameter 2 indicates that the number of decimal places should be displayed. This method returns 99.00
* This method indicates a decimal number with 0 to 20 digits. If the value exceeds this range, an error is thrown.
*/
// Var numberObj = new Number (99 );
// Alert (numberObj. toFixed (2 ));

String type:
[Javascript]
/**
* String class
* The charAt (4) method returns the characters in the string whose index is 4 and the index starts from 0. This method returns "o"
* If you want to get a character code that is not a character, you can call charCodeAt (4). This method returns "111"
* Concat (string1, string2, stringn) This method connects one or more strings to the original value of the String object. The original String object remains unchanged.
* The first parameter of indexOf (searchValue, fromIndex) is the character to be searched, and the second parameter is located at the position of the string,
* The second parameter is optional. The default value of this method is 0 (starting with a string ).
* The lastIndexOf (searchValue, fromIndex) parameter is the same as that of the indexOf method!
* This method is used to start searching at the end of a character,
* Return values of two (indexOf () and lastIndexOf () methods:
* If the character is found, the position of the character string is returned. If the character cannot be found,-1 is returned.
* String truncation: slice (start, end), substring (start, end)
* Details reference: http://www.w3school.com.cn/js/jsref_obj_string.asp
* Case-insensitive conversion:
* ToLocaleLowerCase () converts a string to lowercase.
* ToLocaleUpperCase () converts a string to uppercase.
* ToLowerCase () converts a string to lowercase.
* ToUpperCase () converts a string to uppercase.
*
*/
Var stringObj = new String ("Hello World ");
Var resultObj = stringObj. concat ("string2", "string3", "stringN", "string5 ");
// Alert (resultObj );
// Alert (stringObj. charAt (4 ));
// Alert (stringObj. charCodeAt (4 ));
// Alert (stringObj. indexOf ("l", 7 ));
// Alert (stringObj. indexOf ("l "));
// Alert (stringObj. lastIndexOf ("l", 3 ));
// Alert (stringObj. lastIndexOf ("l "));
// Alert ("5" = 5); // outputs true

Array:
[Javascript]
/**
* Join ();
* The elements in the array are separated by any character.
* Split ();
* Convert a string containing special delimiters (any characters) into an array
* Split (separator, limit );
* Separator: A required parameter and delimiter.
* Limit: optional parameter, cutoff position, and last digit by default
* Concat is the same as the concat method of a string,
* All are added based on the original
* Slice (begin, end) is the same as a string, one is a string index, and the other is an array index.
*
*/
// Var colors = ["red", "blue", "green"];
// Alert (colors. join ("-string -"));
// Alert (colors. join ("-string-"). split ("-string -"));
// Var clo = "green ";
// Alert (clo. split ("", 2 ));
// Clo. split (separator, limit)
// Alert (colors. concat ("yellow", "purple "));
// Alert (colors. slice (1, 3 ));


/**
* Push (element1, elementN)
* This method is used to add one or more items to the end of an array.
* Pop ()
* This method is used to delete the last array (length-1) and return it as the function value.
* Shift ()
* In this method, the user deletes the first array item (0) and returns the value of [0 ].
* Unshift (element1, elementN)
* This method adds one or more items at the beginning of the array.
* Sort ()
* Encoding and sorting by character
*/
// Var stack = new Array ();
// Stack. push ("red ");
// Stack. push ("green", 2 );
// Stack. push ("blue", 1 );
// Alert (stack );
// Alert (stack. pop ());
// Alert (stack. shift ());
// Stack. unshift ("yellow", "purple ")
// Alert (stack. sort ());


Var spliceArr = new Array ("red", 2, 9, 4 );
/*
* Remove the items 0 to 2 from the array.
*/
SpliceArr. splice (0, 2 );
Alert (spliceArr );

/*
* Insert "blue", "yellow", "three" at location 2 to delete two items
*
*/
SpliceArr. splice (1, 2, "blue", "yellow", "three ");
Alert (spliceArr );

From Dan's column